c# - C#6's Improved overload resolution - clarification? -

among new features in c#6, mysterious feature (to me) "improved overload resolution".

maybe it's because couldn't find related info/examples/explanation it.

the 2 remaining features not discussed support defining custom add extension method collection initializers, and minor improved overload resolution

looking @ roslyn wiki

there number of small improvements overload resolution, result in more things working way you’d expect them to. improvements relate “betterness” – way compiler decides of 2 overloads better given argument.

and ask:

question:

how improved overload resolution comes play in c#6? , how different c#5 (example? documentation?)

i believe meant here "better betterness" rules documented in roslyn github repo.

sample code:

using system;  class test {     static void foo(action action) {}     static void foo(func<int> func) {}     static int bar() { return 1; }      static void main()     {         foo(bar);             } } 

using c# 5 compiler (e.g. in c:\windows\microsoft.net\framework\v4.0.30319\) gives 2 errors:

test.cs(11,9): error cs0121: call ambiguous between following methods or properties:
     'test.foo(system.action)' , 'test.foo(system.func)'
test.cs(11,13): error cs0407: 'int test.bar()' has wrong return type

using c# 6 compiler, compiles fine.

likewise using exact matching lambda expressions, generates ambiguous overload error c# 5 compiler, not c# 6:

using system;  class test {     static void foo(func<func<long>> func) {}     static void foo(func<func<int>> func) {}      static void main()     {         foo(() => () => 7);     } }