note the return types of index and range operations#16290
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BillWagner merged 4 commits intodotnet:masterfrom Dec 19, 2019
Merged
note the return types of index and range operations#16290BillWagner merged 4 commits intodotnet:masterfrom
BillWagner merged 4 commits intodotnet:masterfrom
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Provide a brief description of the return types for index and range expressions.
pkulikov
reviewed
Dec 16, 2019
| If a type provides an [indexer](../programming-guide/indexers/index.md) with an <xref:System.Index> or <xref:System.Range> parameter, it explicitly supports indices or ranges respectively. In these cases, the index or range expression returns the type returned by that indexer. | ||
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| A type is **countable** if it has a property named `Length` or `Count` with an accessible getter and a return type of `int`. A countable type that doesn't explicitly support indices or ranges may provide an implicit support for them. For more information, see the [Implicit Index support](~/_csharplang/proposals/csharp-8.0/ranges.md#implicit-index-support) and [Implicit Range support](~/_csharplang/proposals/csharp-8.0/ranges.md#implicit-range-support) sections of the [feature proposal note](~/_csharplang/proposals/csharp-8.0/ranges.md). | ||
| A type is **countable** if it has a property named `Length` or `Count` with an accessible getter and a return type of `int`. A countable type that doesn't explicitly support indices or ranges may provide an implicit support for them. For more information, see the [Implicit Index support](~/_csharplang/proposals/csharp-8.0/ranges.md#implicit-index-support) and [Implicit Range support](~/_csharplang/proposals/csharp-8.0/ranges.md#implicit-range-support) sections of the [feature proposal note](~/_csharplang/proposals/csharp-8.0/ranges.md). An implicit index operator returns the same type as the indexer that takes a single `int` parameter. Range expressions typically return the same type as the left operand of the range expression. |
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An implicit index operator returns the same type as the indexer that takes a single
intparameter.
That might be difficult to process if the links to the spec are not followed. The preceding text in the paragraph doesn't mention the indexer with a single int parameter. I think that sentence can be removed at all. It's almost obvious that index expression has the type of sequence element. The linked issue is about the range expression.
The range expression is not defined. It can be an expression of the form a..b, but I think it's the wrong guess for this paragraph. Most probably, it's s[a..b] then. However, in both cases I would use the "left operand" to refer to a. Can we refer to s as the "source sequence" like in the following suggestion:
Suggested change
| A type is **countable** if it has a property named `Length` or `Count` with an accessible getter and a return type of `int`. A countable type that doesn't explicitly support indices or ranges may provide an implicit support for them. For more information, see the [Implicit Index support](~/_csharplang/proposals/csharp-8.0/ranges.md#implicit-index-support) and [Implicit Range support](~/_csharplang/proposals/csharp-8.0/ranges.md#implicit-range-support) sections of the [feature proposal note](~/_csharplang/proposals/csharp-8.0/ranges.md). An implicit index operator returns the same type as the indexer that takes a single `int` parameter. Range expressions typically return the same type as the left operand of the range expression. | |
| A type is **countable** if it has a property named `Length` or `Count` with an accessible getter and a return type of `int`. A countable type that doesn't explicitly support indices or ranges may provide an implicit support for them. For more information, see the [Implicit Index support](~/_csharplang/proposals/csharp-8.0/ranges.md#implicit-index-support) and [Implicit Range support](~/_csharplang/proposals/csharp-8.0/ranges.md#implicit-range-support) sections of the [feature proposal note](~/_csharplang/proposals/csharp-8.0/ranges.md). An implicit index operator returns the same type as the indexer that takes a single `int` parameter. Range expressions typically return a sequence of the same type as the type of the source sequence. |
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I took your suggestion. I think I should do more here. Another edit round coming soon.
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@pkulikov Let me know what you think of this update.
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@BillWagner LGTM modulo two suggestions, one of which fixes the xref link.
Co-Authored-By: Petr Kulikov <petr.kulikov@gmail.com>
pkulikov
reviewed
Dec 19, 2019
Co-Authored-By: Petr Kulikov <petr.kulikov@gmail.com>
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Provide a brief description of the return types for index and range expressions.
Fixes #15067 (leveraging the changes in dotnet/samples#1620