[Proposal]: Allow default value for out parameter

[heku]

Allow default value for out parameter

• Proposed
• Prototype: Not Started
• Implementation: Not Started
• Specification: Not Started

Summary

Allow default value for out parameter

Motivation

Detailed design

Allow add default value for out parameter so that we can change the code below

bool Method(out string value) {
  if(xxxx){
    value = "xxx";
    return true;
  }
  value = null;
  return false;
}

to

bool Method(out string value = null) {
  if(xxxx){
    value = "xxx";
    return true;
  }
  return false;
}

This feature seems only need C# compiler level update by compiling parameter out string value = null to out string value with one more line at the first of the method body value = null

Drawbacks

Alternatives

Unresolved questions

Design meetings

[YairHalberstadt]

What's the advantage of:

bool Method(out string value = null) {
  if(xxxx){
    value = "xxx";
    return true;
  }
  return false;
}

over

bool Method(out string value) {
  value = null;
  if(xxxx){
    value = "xxx";
    return true;
  }
  return false;
}

[333fred]

I'm going to convert this to a discussion. We generally want proposals to be more complete. Adding more around the motivation here would help sell the idea, as I agree with Yair that I don't see much of a benefit.

[miloush]

Duplicate of dotnet/roslyn#1757 resp. #1033

[YairHalberstadt]

Note that #1033 is championed

[YairHalberstadt]

And was rejected