opMul

[Denton Cockburn]

On Tue, 04 Mar 2008 05:56:57 +0900, Bill Baxter wrote:

> Denton Cockburn wrote:

>> 
>> so what I want is this:
>> 
>> struct Foo
>>  {
>>  	int bar;
>>  	void doStuff(const Foo b)
>>  	{
>>  		bar += b.bar; /* I want an error here */
>>  	}
> 
> You're not changing b, so you're not going to get an error there.

You're right, that was a mistake.

I misphrased my whole query (I misread the compiler error message).
The concern is still there though, here's a sample of code that produces
the message.

struct Foo
{
	int x;
	
	Foo opMul(const Foo b)
	{
		Foo f;
		f.x = x * b.x;
		
		return f;
	}
}

void main()
{
	Foo f;
	Foo y;
	f.x = 6;
	y.x = 7;
	
	const(Foo) t = f;
	Foo p = t * y;
}

produces this error:
test.d(24): function test.Foo.opMul (const(Foo)) does not match parameter types (Foo)
test.d(24): Error: t.opMul can only be called on a mutable object, not const(Foo)


So my question SHOULD have been:

Why can't opMul et al be called on a constant object (reference)?

Sorry for the previous confusion.