Bug 10663 - Compiler should rewrite lambdas that are direct delegate invocations into direct delegate invocations
Summary: Compiler should rewrite lambdas that are direct delegate invocations into dir...
Status: RESOLVED FIXED
Alias: None
Product: Compilers
Classification: Mono
Component: C# ()
Version: unspecified
Hardware: PC Mac OS
: Low enhancement
Target Milestone: ---
Assignee: Marek Safar
URL:
Depends on:
Blocks:
 
Reported: 2013-02-25 17:52 UTC by Bojan Rajkovic [MSFT]
Modified: 2013-03-15 10:30 UTC (History)
1 user (show)

Tags:
Is this bug a regression?: ---
Last known good build:

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Status:
RESOLVED FIXED

Description Bojan Rajkovic [MSFT] 2013-02-25 17:52:41 UTC
It would be nice if the compiler could, when possible, rewrite simple wrapper lambdas that are just invocations of a method into direct delegate invocations. For example, consider the following code:

using System;

class Test
{
  public static void Main (string[] args)
  {
    Array.Sort (args, (a, b) => String.Compare (a, b));
    foreach (var arg in args)
      {
        Console.WriteLine (arg);
      }
  }
}

Here, the (a, b) => String.Compare (a, b) is totally superfluous. This code is better written as:

using System;

class Test
{
  public static void Main (string[] args)
  {
    Array.Sort (args, String.Compare);
    foreach (var arg in args)
      {
        Console.WriteLine (arg);
      }
  }
}

The IL emitted is totally different as well—when using the wrapper lambda, the IL is more complex, and likely there's some performance hit due to the extra method call.
Comment 1 Marek Safar 2013-03-15 10:30:54 UTC
Implemented in master, good suggestion was surprised it was used quite often.

Requires optimisations to be enabled or it'd constrain debugging experience.