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Improve pattern matching and switch notes

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Marcello 2021-10-04 21:52:08 +02:00
parent 02c0a04aad
commit 29c6b2a5c7
1 changed files with 31 additions and 53 deletions
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DotNet/C#/C#.md
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@ -796,6 +796,35 @@ else
} }
``` ```
### Pattern Matching
[Pattern Matching](https://docs.microsoft.com/en-us/dotnet/csharp/pattern-matching)
A pattern describes one or more criteria that a value can be tested against. It's usable in switch statements, switch expressions and if statements.
```cs
<expr> is Type t // type pattern
<expr> is (Type X, Type Y): // positional pattern
<expr> is (Type X, _): // positional pattern + discard pattern
<expr> is Type {Property: value}: // property patten (check Type and that the property has a certain value)
<expr> is Type {Property: value} p: // property patten with output (variable p is usable in the block)
// constant pattern
<expr> is literalValue // e.g. 1, 'c', "literal"
<expr> is CONSTANT
<expr> is Enum.Value
// C# 9+
<expr> is pattern and pattern
<expr> is pattern or pattern
<expr> is not pattern
<expr> is { Property: > value } // works with all comparison operators
<expr> is > value // works with all comparison operators
// C# 10+
<expr> is { Property.InnerProperty: value } // match in nested properties
```
### Switch ### Switch
The `when` keyword can be used to specify a filter condition that causes its associated case label to be true only if the filter condition is also true. The `when` keyword can be used to specify a filter condition that causes its associated case label to be true only if the filter condition is also true.
@ -819,25 +848,7 @@ switch (expr)
// code here // code here
break; break;
case Type t: // if expr matches Type result is stored in t local variable to be used in the block // cases using pattern matching
// code here
break;
case value when(condition):
// code here
break;
case < value:
// code here
break;
case <= value and >= value:
// code here
break;
case > value:
// code here
break;
default: default:
// code here // code here
@ -849,43 +860,10 @@ variable switch
{ {
key_1 => value, key_1 => value,
key_2 => value, key_2 => value,
// cases using pattern matching
... ...
_ => default_value // underscore (_) discard pattern as default case _ => default_value // underscore (_) discard pattern as default case
}; };
Type func(Type input){
return input switch
{
key_1 => value,
key_2 => value,
...,
_ => default_value // underscore (_) discard pattern as default case
};
}
```
### Pattern Matching
[Pattern Matching](https://docs.microsoft.com/en-us/dotnet/csharp/pattern-matching)
A pattern describes one or more criteria that a value can be tested against.
```cs
<expr> is Type t // type pattern
<expr> is (Type X, Type Y): // positional pattern
<expr> is (Type X, _): // positional pattern + discard pattern
<expr> is Type {Property : value}: // property patten (check Type and that the property has a certain value)
<expr> is Type {Property : value} p: // property patten with output (variable p is usable in the block)
// constant pattern
<expr> is literalValue // e.g. 1, 'c', "literal"
<expr> is CONSTANT
<expr> is Enum.Value
// C# 9+
<expr> is pattern and pattern
<expr> is pattern or pattern
<expr> is not pattern
``` ```
## Loop Statements ## Loop Statements