maxmustermann/csharplang
1
0
Fork 0
Code Issues Pull requests Projects Releases Wiki Activity

Specify equality operators for records (#3754)

Browse source 
See https://github.com/dotnet/csharplang/blob/master/meetings/2020/LDM-2020-07-27.md#conclusion-1
This commit is contained in:
AlekseyTs 2020-07-31 10:49:11 -07:00 committed by GitHub
parent a4a9e017df
commit cd3c18237b
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
1 changed files with 23 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

25
proposals/csharp-9.0/records.md
View file

@ -33,7 +33,7 @@ Record parameters cannot use `ref`, `out` or `this` modifiers (but `in` and `par
## Inheritance
Records cannot inherit from classes, unless the class is `object`, and classes cannot inherit from records.
Records cannot inherit from classes, unless the class is `object`, and classes cannot inherit from records. Records can inherit from other records.
## Members of a record type
@ -76,6 +76,15 @@ The synthesized `Equals(R?)` returns `true` if and only if each of the following
- If there is a base record type, the value of `base.Equals(other)` (a non-virtual call to `public virtual bool Equals(Base? other)`); otherwise
the value of `EqualityContract == other.EqualityContract`.
The record type includes synthesized `==` and `!=` operators equivalent to operators declared as follows:
```C#
pubic static bool operator==(R? r1, R? r2)
=> (object)r1 == r2 || (r1?.Equals(r2) ?? false);
public static bool operator!=(R? r1, R? r2)
=> !(r1 == r2);
```
The `Equals` method called by the `==` operator is the `Equals(R? other)` method specified above. The `!=` operator delegates to the `==` operator. It is an error if the operators are declared explicitly.
If the record type is derived from a base record type `Base`, the record type includes a synthesized override equivalent to a method declared as follows:
```C#
public sealed override bool Equals(Base? other);
@ -109,7 +118,7 @@ For example, consider the following record types:
```C#
record R1(T1 P1);
record R2(T1 P1, T2 P2) : R1(P1);
record R2(T1 P1, T2 P2, T3 P3) : R2(P1, P2);
record R3(T1 P1, T2 P2, T3 P3) : R2(P1, P2);
```
For those record types, the synthesized members would be something like:
@ -125,6 +134,10 @@ class R1 : IEquatable<R1>
EqualityContract == other.EqualityContract &&
EqualityComparer<T1>.Default.Equals(P1, other.P1);
}
pubic static bool operator==(R1? r1, R1? r2)
=> (object)r1 == r2 || (r1?.Equals(r2) ?? false);
public static bool operator!=(R1? r1, R1? r2)
=> !(r1 == r2);
public override int GetHashCode()
{
return Combine(EqualityComparer<Type>.Default.GetHashCode(EqualityContract),
@ -143,6 +156,10 @@ class R2 : R1, IEquatable<R2>
return base.Equals((R1?)other) &&
EqualityComparer<T2>.Default.Equals(P2, other.P2);
}
pubic static bool operator==(R2? r1, R2? r2)
=> (object)r1 == r2 || (r1?.Equals(r2) ?? false);
public static bool operator!=(R2? r1, R2? r2)
=> !(r1 == r2)`;
public override int GetHashCode()
{
return Combine(base.GetHashCode(),
@ -161,6 +178,10 @@ class R3 : R2, IEquatable<R3>
return base.Equals((R2?)other) &&
EqualityComparer<T3>.Default.Equals(P3, other.P3);
}
pubic static bool operator==(R3? r1, R3? r2)
=> (object)r1 == r2 || (r1?.Equals(r2) ?? false);
public static bool operator!=(R3? r1, R3? r2)
=> !(r1 == r2);
public override int GetHashCode()
{
return Combine(base.GetHashCode(),