Why doesn't the new hat-operator index from the C# 8 array-slicing feature start at 0?












70














C# 8.0 introduces a convenient way to slice arrays - see official C# 8.0 blogpost.



The syntax to access the last element of an array is



int value = { 10, 11, 12, 13 };

int a = value[^1]; // 13
int b = value[^2]; // 12


I'm wondering why the indexing for accessing the elements backwards starts at 1 instead of 0? Is there a technical reason for this?










share|improve this question




















  • 6




    Note that C++ ranges are also [beginInclusive, endExclusive). It is a common convention.
    – bommelding
    23 hours ago








  • 2




    @Sinatr: Based on that blog post, the syntax to return everything would be value[0..^0], since the ending index is exclusive (which is how most other languages work, too). Also, conveniently, value[^i..^0] will give you the last i items.
    – BlueRaja - Danny Pflughoeft
    18 hours ago










  • @bommelding: C++ rbegin() somewhat disagrees with that notion -- the first item out of that range isn't the one-beyond-the-end either. ;-)
    – DevSolar
    26 mins ago
















70














C# 8.0 introduces a convenient way to slice arrays - see official C# 8.0 blogpost.



The syntax to access the last element of an array is



int value = { 10, 11, 12, 13 };

int a = value[^1]; // 13
int b = value[^2]; // 12


I'm wondering why the indexing for accessing the elements backwards starts at 1 instead of 0? Is there a technical reason for this?










share|improve this question




















  • 6




    Note that C++ ranges are also [beginInclusive, endExclusive). It is a common convention.
    – bommelding
    23 hours ago








  • 2




    @Sinatr: Based on that blog post, the syntax to return everything would be value[0..^0], since the ending index is exclusive (which is how most other languages work, too). Also, conveniently, value[^i..^0] will give you the last i items.
    – BlueRaja - Danny Pflughoeft
    18 hours ago










  • @bommelding: C++ rbegin() somewhat disagrees with that notion -- the first item out of that range isn't the one-beyond-the-end either. ;-)
    – DevSolar
    26 mins ago














70












70








70


11





C# 8.0 introduces a convenient way to slice arrays - see official C# 8.0 blogpost.



The syntax to access the last element of an array is



int value = { 10, 11, 12, 13 };

int a = value[^1]; // 13
int b = value[^2]; // 12


I'm wondering why the indexing for accessing the elements backwards starts at 1 instead of 0? Is there a technical reason for this?










share|improve this question















C# 8.0 introduces a convenient way to slice arrays - see official C# 8.0 blogpost.



The syntax to access the last element of an array is



int value = { 10, 11, 12, 13 };

int a = value[^1]; // 13
int b = value[^2]; // 12


I'm wondering why the indexing for accessing the elements backwards starts at 1 instead of 0? Is there a technical reason for this?







c# arrays c#-8.0






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 4 hours ago









Martin Zikmund

23.4k43460




23.4k43460










asked 23 hours ago









Michael PittinoMichael Pittino

4251614




4251614








  • 6




    Note that C++ ranges are also [beginInclusive, endExclusive). It is a common convention.
    – bommelding
    23 hours ago








  • 2




    @Sinatr: Based on that blog post, the syntax to return everything would be value[0..^0], since the ending index is exclusive (which is how most other languages work, too). Also, conveniently, value[^i..^0] will give you the last i items.
    – BlueRaja - Danny Pflughoeft
    18 hours ago










  • @bommelding: C++ rbegin() somewhat disagrees with that notion -- the first item out of that range isn't the one-beyond-the-end either. ;-)
    – DevSolar
    26 mins ago














  • 6




    Note that C++ ranges are also [beginInclusive, endExclusive). It is a common convention.
    – bommelding
    23 hours ago








  • 2




    @Sinatr: Based on that blog post, the syntax to return everything would be value[0..^0], since the ending index is exclusive (which is how most other languages work, too). Also, conveniently, value[^i..^0] will give you the last i items.
    – BlueRaja - Danny Pflughoeft
    18 hours ago










  • @bommelding: C++ rbegin() somewhat disagrees with that notion -- the first item out of that range isn't the one-beyond-the-end either. ;-)
    – DevSolar
    26 mins ago








6




6




Note that C++ ranges are also [beginInclusive, endExclusive). It is a common convention.
– bommelding
23 hours ago






Note that C++ ranges are also [beginInclusive, endExclusive). It is a common convention.
– bommelding
23 hours ago






2




2




@Sinatr: Based on that blog post, the syntax to return everything would be value[0..^0], since the ending index is exclusive (which is how most other languages work, too). Also, conveniently, value[^i..^0] will give you the last i items.
– BlueRaja - Danny Pflughoeft
18 hours ago




@Sinatr: Based on that blog post, the syntax to return everything would be value[0..^0], since the ending index is exclusive (which is how most other languages work, too). Also, conveniently, value[^i..^0] will give you the last i items.
– BlueRaja - Danny Pflughoeft
18 hours ago












@bommelding: C++ rbegin() somewhat disagrees with that notion -- the first item out of that range isn't the one-beyond-the-end either. ;-)
– DevSolar
26 mins ago




@bommelding: C++ rbegin() somewhat disagrees with that notion -- the first item out of that range isn't the one-beyond-the-end either. ;-)
– DevSolar
26 mins ago












1 Answer
1






active

oldest

votes


















95














Official answer



For better visibility, here is a comment from Mads Torgersen explaining this design decision from the C# 8 blogpost:




We decided to follow Python when it comes to the from-beginning and from-end arithmetic. 0 designates the first element (as always), and ^0 the “length’th” element, i.e. the one right off the end. That way you get a simple relationship, where an elements position from beginning plus its position from end equals the length. the x in ^x is what you would have subtracted from the length if you’d done the math yourself.



Why not use minus (-) instead of the new hat (^) operator? This primarily has to do with ranges. Again in keeping with Python and most of the industry, we want our ranges to be inclusive at the beginning, exclusive at the end. What is the index you pass to say that a range should go all the way to the end? In C# the answer is simple: x..^0 goes from x to the end. In Python there is no explicit index you can give: -0 doesn’t work, because it is equal to 0, the first element! So in Python you have to leave the end index off completely to express a range that goes to the end: x... If the end of the range is computed, then you need to remember to have special logic in case it comes out to 0. As in x..-y, where y was computed and came out to 0. This is a common nuisance and source of bugs.



Finally, note that indices and ranges are first class types in .NET/C#. Their behavior is not tied to what they are applied to, or even to being used in an indexer. You can totally define your own indexer that takes Index and another one that takes Range – and we’re going to add such indexers to e.g. Span. But you can also have methods that take ranges, for instance.




My answer



I think this is to match the classic syntax we are used to:



value[^1] == value[value.Length - 1]


If it used 0, it would be confusing when the two syntaxes were used side-by-side. This way it has lower cognitive load.



Other languages like Python also use the same convention.






share|improve this answer



















  • 8




    Minor correction to Mads comment: you do not have to leave off the end index completely in python. You can use None in place of a number: [0,1,2,3,4][2:None] == [2,3,4]. But, yes you cannot use an integer as end index (without computing the length obviously).
    – Giacomo Alzetta
    20 hours ago








  • 4




    Wait.. what's wrong with x..? That seems fine and I've never had problem with the python [3:] syntax.
    – mowwwalker
    15 hours ago






  • 2




    @mowwwalker nothing wrong. I seems that x.. syntax will be supported too. It's in example of ranges proposal
    – Mariusz Pawelski
    12 hours ago








  • 1




    @mowwwalker - isn't that already covered in the quote? "So in Python ... If the end of the range is computed, then you need to remember to have special logic in case it comes out to 0"
    – Damien_The_Unbeliever
    4 hours ago











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1 Answer
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1 Answer
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active

oldest

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active

oldest

votes









95














Official answer



For better visibility, here is a comment from Mads Torgersen explaining this design decision from the C# 8 blogpost:




We decided to follow Python when it comes to the from-beginning and from-end arithmetic. 0 designates the first element (as always), and ^0 the “length’th” element, i.e. the one right off the end. That way you get a simple relationship, where an elements position from beginning plus its position from end equals the length. the x in ^x is what you would have subtracted from the length if you’d done the math yourself.



Why not use minus (-) instead of the new hat (^) operator? This primarily has to do with ranges. Again in keeping with Python and most of the industry, we want our ranges to be inclusive at the beginning, exclusive at the end. What is the index you pass to say that a range should go all the way to the end? In C# the answer is simple: x..^0 goes from x to the end. In Python there is no explicit index you can give: -0 doesn’t work, because it is equal to 0, the first element! So in Python you have to leave the end index off completely to express a range that goes to the end: x... If the end of the range is computed, then you need to remember to have special logic in case it comes out to 0. As in x..-y, where y was computed and came out to 0. This is a common nuisance and source of bugs.



Finally, note that indices and ranges are first class types in .NET/C#. Their behavior is not tied to what they are applied to, or even to being used in an indexer. You can totally define your own indexer that takes Index and another one that takes Range – and we’re going to add such indexers to e.g. Span. But you can also have methods that take ranges, for instance.




My answer



I think this is to match the classic syntax we are used to:



value[^1] == value[value.Length - 1]


If it used 0, it would be confusing when the two syntaxes were used side-by-side. This way it has lower cognitive load.



Other languages like Python also use the same convention.






share|improve this answer



















  • 8




    Minor correction to Mads comment: you do not have to leave off the end index completely in python. You can use None in place of a number: [0,1,2,3,4][2:None] == [2,3,4]. But, yes you cannot use an integer as end index (without computing the length obviously).
    – Giacomo Alzetta
    20 hours ago








  • 4




    Wait.. what's wrong with x..? That seems fine and I've never had problem with the python [3:] syntax.
    – mowwwalker
    15 hours ago






  • 2




    @mowwwalker nothing wrong. I seems that x.. syntax will be supported too. It's in example of ranges proposal
    – Mariusz Pawelski
    12 hours ago








  • 1




    @mowwwalker - isn't that already covered in the quote? "So in Python ... If the end of the range is computed, then you need to remember to have special logic in case it comes out to 0"
    – Damien_The_Unbeliever
    4 hours ago
















95














Official answer



For better visibility, here is a comment from Mads Torgersen explaining this design decision from the C# 8 blogpost:




We decided to follow Python when it comes to the from-beginning and from-end arithmetic. 0 designates the first element (as always), and ^0 the “length’th” element, i.e. the one right off the end. That way you get a simple relationship, where an elements position from beginning plus its position from end equals the length. the x in ^x is what you would have subtracted from the length if you’d done the math yourself.



Why not use minus (-) instead of the new hat (^) operator? This primarily has to do with ranges. Again in keeping with Python and most of the industry, we want our ranges to be inclusive at the beginning, exclusive at the end. What is the index you pass to say that a range should go all the way to the end? In C# the answer is simple: x..^0 goes from x to the end. In Python there is no explicit index you can give: -0 doesn’t work, because it is equal to 0, the first element! So in Python you have to leave the end index off completely to express a range that goes to the end: x... If the end of the range is computed, then you need to remember to have special logic in case it comes out to 0. As in x..-y, where y was computed and came out to 0. This is a common nuisance and source of bugs.



Finally, note that indices and ranges are first class types in .NET/C#. Their behavior is not tied to what they are applied to, or even to being used in an indexer. You can totally define your own indexer that takes Index and another one that takes Range – and we’re going to add such indexers to e.g. Span. But you can also have methods that take ranges, for instance.




My answer



I think this is to match the classic syntax we are used to:



value[^1] == value[value.Length - 1]


If it used 0, it would be confusing when the two syntaxes were used side-by-side. This way it has lower cognitive load.



Other languages like Python also use the same convention.






share|improve this answer



















  • 8




    Minor correction to Mads comment: you do not have to leave off the end index completely in python. You can use None in place of a number: [0,1,2,3,4][2:None] == [2,3,4]. But, yes you cannot use an integer as end index (without computing the length obviously).
    – Giacomo Alzetta
    20 hours ago








  • 4




    Wait.. what's wrong with x..? That seems fine and I've never had problem with the python [3:] syntax.
    – mowwwalker
    15 hours ago






  • 2




    @mowwwalker nothing wrong. I seems that x.. syntax will be supported too. It's in example of ranges proposal
    – Mariusz Pawelski
    12 hours ago








  • 1




    @mowwwalker - isn't that already covered in the quote? "So in Python ... If the end of the range is computed, then you need to remember to have special logic in case it comes out to 0"
    – Damien_The_Unbeliever
    4 hours ago














95












95








95






Official answer



For better visibility, here is a comment from Mads Torgersen explaining this design decision from the C# 8 blogpost:




We decided to follow Python when it comes to the from-beginning and from-end arithmetic. 0 designates the first element (as always), and ^0 the “length’th” element, i.e. the one right off the end. That way you get a simple relationship, where an elements position from beginning plus its position from end equals the length. the x in ^x is what you would have subtracted from the length if you’d done the math yourself.



Why not use minus (-) instead of the new hat (^) operator? This primarily has to do with ranges. Again in keeping with Python and most of the industry, we want our ranges to be inclusive at the beginning, exclusive at the end. What is the index you pass to say that a range should go all the way to the end? In C# the answer is simple: x..^0 goes from x to the end. In Python there is no explicit index you can give: -0 doesn’t work, because it is equal to 0, the first element! So in Python you have to leave the end index off completely to express a range that goes to the end: x... If the end of the range is computed, then you need to remember to have special logic in case it comes out to 0. As in x..-y, where y was computed and came out to 0. This is a common nuisance and source of bugs.



Finally, note that indices and ranges are first class types in .NET/C#. Their behavior is not tied to what they are applied to, or even to being used in an indexer. You can totally define your own indexer that takes Index and another one that takes Range – and we’re going to add such indexers to e.g. Span. But you can also have methods that take ranges, for instance.




My answer



I think this is to match the classic syntax we are used to:



value[^1] == value[value.Length - 1]


If it used 0, it would be confusing when the two syntaxes were used side-by-side. This way it has lower cognitive load.



Other languages like Python also use the same convention.






share|improve this answer














Official answer



For better visibility, here is a comment from Mads Torgersen explaining this design decision from the C# 8 blogpost:




We decided to follow Python when it comes to the from-beginning and from-end arithmetic. 0 designates the first element (as always), and ^0 the “length’th” element, i.e. the one right off the end. That way you get a simple relationship, where an elements position from beginning plus its position from end equals the length. the x in ^x is what you would have subtracted from the length if you’d done the math yourself.



Why not use minus (-) instead of the new hat (^) operator? This primarily has to do with ranges. Again in keeping with Python and most of the industry, we want our ranges to be inclusive at the beginning, exclusive at the end. What is the index you pass to say that a range should go all the way to the end? In C# the answer is simple: x..^0 goes from x to the end. In Python there is no explicit index you can give: -0 doesn’t work, because it is equal to 0, the first element! So in Python you have to leave the end index off completely to express a range that goes to the end: x... If the end of the range is computed, then you need to remember to have special logic in case it comes out to 0. As in x..-y, where y was computed and came out to 0. This is a common nuisance and source of bugs.



Finally, note that indices and ranges are first class types in .NET/C#. Their behavior is not tied to what they are applied to, or even to being used in an indexer. You can totally define your own indexer that takes Index and another one that takes Range – and we’re going to add such indexers to e.g. Span. But you can also have methods that take ranges, for instance.




My answer



I think this is to match the classic syntax we are used to:



value[^1] == value[value.Length - 1]


If it used 0, it would be confusing when the two syntaxes were used side-by-side. This way it has lower cognitive load.



Other languages like Python also use the same convention.







share|improve this answer














share|improve this answer



share|improve this answer








edited 4 hours ago

























answered 23 hours ago









Martin ZikmundMartin Zikmund

23.4k43460




23.4k43460








  • 8




    Minor correction to Mads comment: you do not have to leave off the end index completely in python. You can use None in place of a number: [0,1,2,3,4][2:None] == [2,3,4]. But, yes you cannot use an integer as end index (without computing the length obviously).
    – Giacomo Alzetta
    20 hours ago








  • 4




    Wait.. what's wrong with x..? That seems fine and I've never had problem with the python [3:] syntax.
    – mowwwalker
    15 hours ago






  • 2




    @mowwwalker nothing wrong. I seems that x.. syntax will be supported too. It's in example of ranges proposal
    – Mariusz Pawelski
    12 hours ago








  • 1




    @mowwwalker - isn't that already covered in the quote? "So in Python ... If the end of the range is computed, then you need to remember to have special logic in case it comes out to 0"
    – Damien_The_Unbeliever
    4 hours ago














  • 8




    Minor correction to Mads comment: you do not have to leave off the end index completely in python. You can use None in place of a number: [0,1,2,3,4][2:None] == [2,3,4]. But, yes you cannot use an integer as end index (without computing the length obviously).
    – Giacomo Alzetta
    20 hours ago








  • 4




    Wait.. what's wrong with x..? That seems fine and I've never had problem with the python [3:] syntax.
    – mowwwalker
    15 hours ago






  • 2




    @mowwwalker nothing wrong. I seems that x.. syntax will be supported too. It's in example of ranges proposal
    – Mariusz Pawelski
    12 hours ago








  • 1




    @mowwwalker - isn't that already covered in the quote? "So in Python ... If the end of the range is computed, then you need to remember to have special logic in case it comes out to 0"
    – Damien_The_Unbeliever
    4 hours ago








8




8




Minor correction to Mads comment: you do not have to leave off the end index completely in python. You can use None in place of a number: [0,1,2,3,4][2:None] == [2,3,4]. But, yes you cannot use an integer as end index (without computing the length obviously).
– Giacomo Alzetta
20 hours ago






Minor correction to Mads comment: you do not have to leave off the end index completely in python. You can use None in place of a number: [0,1,2,3,4][2:None] == [2,3,4]. But, yes you cannot use an integer as end index (without computing the length obviously).
– Giacomo Alzetta
20 hours ago






4




4




Wait.. what's wrong with x..? That seems fine and I've never had problem with the python [3:] syntax.
– mowwwalker
15 hours ago




Wait.. what's wrong with x..? That seems fine and I've never had problem with the python [3:] syntax.
– mowwwalker
15 hours ago




2




2




@mowwwalker nothing wrong. I seems that x.. syntax will be supported too. It's in example of ranges proposal
– Mariusz Pawelski
12 hours ago






@mowwwalker nothing wrong. I seems that x.. syntax will be supported too. It's in example of ranges proposal
– Mariusz Pawelski
12 hours ago






1




1




@mowwwalker - isn't that already covered in the quote? "So in Python ... If the end of the range is computed, then you need to remember to have special logic in case it comes out to 0"
– Damien_The_Unbeliever
4 hours ago




@mowwwalker - isn't that already covered in the quote? "So in Python ... If the end of the range is computed, then you need to remember to have special logic in case it comes out to 0"
– Damien_The_Unbeliever
4 hours ago


















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