Macro std_x::fn_rename

macro_rules! fn_rename {
    (
      @Prefix { $( $Prefix : tt )* }
      @Name { $Name : ident }
      @Postfix
      {
        fn $OldName : ident
        $( $Postfix : tt )*
      }
    ) => { ... };
    (
      @Prefix { $( $Prefix : tt )* }
      @Name { $Name : ident }
      @Postfix
      {
        $First : tt
        $( $Postfix : tt )*
      }
    ) => { ... };
    (
      @Name { $Name : ident }
      @Fn { $( $Fn : tt )* }
    ) => { ... };
}

Macro to rename function.