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Update the ranges.md file to correctly represent the actual impl. (#3645)

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David Pine 2020-07-07 09:51:45 -05:00 committed by GitHub
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proposals/csharp-8.0/ranges.md
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@ -79,7 +79,7 @@ unary_expression
We call this the *index from end* operator. The predefined *index from end* operators are as follows:
```csharp
System.Index operator ^(int fromEnd);
System.Index operator ^(int fromEnd);
```
The behavior of this operator is only defined for input values greater than or equal to zero.
@ -87,10 +87,9 @@ The behavior of this operator is only defined for input values greater than or e
Examples:
```csharp
var thirdItem = list[2]; // list[2]
var lastItem = list[^1]; // list[Index.CreateFromEnd(1)]
var multiDimensional = list[3, ^2] // list[3, Index.CreateFromEnd(2)]
var array = new int[] { 1, 2, 3, 4, 5 };
var thirdItem = array[2]; // array[2]
var lastItem = array[^1]; // array[new Index(1, fromEnd: true)]
```
#### System.Range
@ -115,26 +114,25 @@ multiplicative_expression
;
```
All forms of the *range operator* have the same precedence. This new precedence group is lower than the *unary operators* and higher than the *mulitiplicative arithmetic operators*.
All forms of the *range operator* have the same precedence. This new precedence group is lower than the *unary operators* and higher than the *multiplicative arithmetic operators*.
We call the `..` operator the *range operator*. The built-in range operator can roughly be understood to correspond to the invocation of a built-in operator of this form:
```csharp
System.Range operator ..(Index start = 0, Index end = ^0);
System.Range operator ..(Index start = 0, Index end = ^0);
```
Examples:
```csharp
var slice1 = list[2..^3]; // list[Range.Create(2, Index.CreateFromEnd(3))]
var slice2 = list[..^3]; // list[Range.ToEnd(Index.CreateFromEnd(3))]
var slice3 = list[2..]; // list[Range.FromStart(2)]
var slice4 = list[..]; // list[Range.All]
var multiDimensional = list[1..2, ..] // list[Range.Create(1, 2), Range.All]
var array = new int[] { 1, 2, 3, 4, 5 };
var slice1 = array[2..^3]; // array[new Range(2, new Index(3, fromEnd: true))]
var slice2 = array[..^3]; // array[Range.EndAt(new Index(3, fromEnd: true))]
var slice3 = array[2..]; // array[Range.StartAt(2)]
var slice4 = array[..]; // array[Range.All]
```
Moreover, `System.Index` should have an implicit conversion from `System.Int32`, in order not to need to overload for mixing integers and indexes over multi-dimensional signatures.
Moreover, `System.Index` should have an implicit conversion from `System.Int32`, in order to avoid the need to overload mixing integers and indexes over multi-dimensional signatures.
## Adding Index and Range support to existing library types
@ -364,8 +362,12 @@ Restrictions:
- The Slice method used for the Range pattern must have exactly two int parameters
- When looking for the pattern members, we look for original definitions, not constructed members
## Design Meetings
## Design meetings
- https://github.com/dotnet/csharplang/blob/master/meetings/2019/LDM-2019-04-01.md
## Questions
- [Jan 10, 2018](https://github.com/dotnet/csharplang/blob/master/meetings/2018/LDM-2018-01-10.md)
- [Jan 18, 2018](https://github.com/dotnet/csharplang/blob/master/meetings/2018/LDM-2018-01-18.md)
- [Jan 22, 2018](https://github.com/dotnet/csharplang/blob/master/meetings/2018/LDM-2018-01-22.md)
- [Dec 3, 2018](https://github.com/dotnet/csharplang/blob/master/meetings/2018/LDM-2018-12-03.md)
- [Mar 25, 2019](https://github.com/dotnet/csharplang/blob/master/meetings/2019/LDM-2019-03-25.md#pattern-based-indexing-with-index-and-range)
- [April 1st, 2019](https://github.com/dotnet/csharplang/blob/master/meetings/2019/LDM-2019-04-01.md)
- [April 15, 2019](https://github.com/dotnet/csharplang/blob/master/meetings/2019/LDM-2019-04-15.md#follow-up-decisions-for-pattern-based-indexrange)