Optimized replace operator

[dmitriyse]

Current State

C# already has a ternary operator, switch expression, and null-coalescing (??) operators.
However, these constructs don't cover the following widespread use case well.
Ternary expression syntax (already works):

string myVariable = otherVar == string.Empty ? null: otherVar;

switch expression syntax (already works):

string myVariable = switch otherVar { string.Empty => null,  _ =>otherVar};

null-coalescing (??) operator, works only for nullability checks:

string myValue = otherVar ?? string.Empty; // No way to use different condition other than "is null"

Proposal:

Optimized syntax (proposal):

string myVariable = otherVar |? string.Empty => null;

Or in general (proposal):

result = value |? {pattern-matching} => replacement;

Alternative:

result = value when  {pattern-matching} => replacement;

[huoyaoyuan]

Coalescing other values is much less common than nulls.

Moreover, comparing with null is well defined for reference types and nullable types, but for other values it may not be.

[ufcpp]

#7880 #7280 #6584