The following program runs correctly

import std.stdio;
int afunction(int x){return x;};
void main()
{
		alias myint = int;
		myint i=5;
		alias tfunction = int function(int);
		tfunction f = & afunction;
		writeln(f(1));
}

This does not:

import std.stdio;
void main()
{
		int afunction(int x){return x;};
		alias myint = int;
		myint i=5;
		alias tfunction = int function(int);
		tfunction f = & afunction;
		writeln(f(1));
}

It gives compile error :
Error: cannot implicitly convert expression &afunction of type int delegate(int x) pure nothrow @nogc @safe to int function(int)

On Monday, 10 May 2021 at 01:25:10 UTC, Alain De Vos wrote:

import std.stdio;
void main()
{
		int afunction(int x){return x;};

            it's not static so -> context -> delegate

  alias myint = int;
  myint i=5;
  alias tfunction = int function(int);
  tfunction f = & afunction;
  writeln(f(1));

It gives compile error :
Error: cannot implicitly convert expression &afunction of type int delegate(int x) pure nothrow @nogc @safe to int function(int)

add static in the second case.

I wonder why ?

I see.
Just like in Java.

This one runs fine,

import std.stdio;
void main()
{
		static int Gfunction(int x){return x;}
		int Lfunction(int x){return x;}
		alias gfunction = int function(int);
		alias lfunction = int delegate(int);
		gfunction g = & Gfunction;
		lfunction l = & Lfunction;
		writeln(g(1));
		writeln(l(1));
}