On Sunday, 4 April 2021 at 18:05:04 UTC, tsbockman wrote:
```
[...]
You cannot assign void returned from bar() as parameter to
opAssign(). The lazy keyword creates some internal delegate,
thus opAssign() works instead.
[...]
auto bar (int i) {
return () {
if (i == 1)
throw new E ("E");
};
}
```
You changed the definition of ``bar`` while the exception
collector (``EC``) is meant to catch and collect an exception
thrown from the *unmodified* function. It seems that the operator
``+=`` or ``~=`` may be better suited to express that intent.
Rewriting this in terms of ``opOpAssign`` works as expected:
```
import std.stdio;
struct EC {
Exception [] ex;
auto opOpAssign (string op: "+", X: void) (lazy X f)
{
writeln (__PRETTY_FUNCTION__);
try return f (); catch (Exception e) ex ~= e;
}
auto opOpAssign (string op: "~", X: void) (lazy X f)
{
writeln (__PRETTY_FUNCTION__);
try return f (); catch (Exception e) ex ~= e;
}
}
class E : Exception { this (string s) { super (s); } }
void bar (int i) { if (i == 1) throw new E ("E"); }
void main ()
{
EC ec;
ec.opOpAssign!"+" (bar (1)); // okay
ec += bar (1); // okay
ec ~= bar (1); // okay
ec.writeln;
}
```
