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digitalmars.D.bugs - strange behavior in opApply

reply BCS <ao pathlink.com> writes:
I think this is a bug. I am not sure, but it is really annoying.

The following code fails to compile:

struct Foo
{
  int opApply(int delegate(in int) dg)
  {
    for(int i = 0; i< 10; i++)
      if(int ret = dg(i>>2))
        return ret;
    return 0;
  }
}

void main()
{
  Foo f;
  int j=0;
  foreach(int i; f)
  {
    j+=i;
  }
}

The foreach body is turned into a delegate taking (inout int), but it is 
not marked as inout! I have a case where I'm trying to use opApply where 
it can't be inout. 

Is this a bug?
Jan 27 2007
parent reply Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:
BCS wrote:
 The foreach body is turned into a delegate taking (inout int), but it is 
 not marked as inout! I have a case where I'm trying to use opApply where 
 it can't be inout.
 Is this a bug?

According to the spec, the signature of opApply must be "int opApply(int delegate(inout Type [, ...]) dg);", so it's actually a bug in your code that the delegate's parameter it isn't marked inout. (unless of course you prefer to consider it a 'bug' in the spec that it's not allowed to be marked 'in' :) )
Jan 27 2007
parent BCS <ao pathlink.com> writes:
Reply to Frits,

 BCS wrote:
 
 The foreach body is turned into a delegate taking (inout int), but it
 is not marked as inout! I have a case where I'm trying to use opApply
 where it can't be inout. Is this a bug?

According to the spec, the signature of opApply must be "int opApply(int delegate(inout Type [, ...]) dg);", so it's actually a bug in your code that the delegate's parameter it isn't marked inout.

Hm.. Is that new? I shure, it used to allow "in".
 (unless of course you prefer to consider it a 'bug' in the spec that
 it's not allowed to be marked 'in' :) )
 

Yeah, I guess I'll have to stick with that approach. What else am I to do in a "must not modify data" loop? Copy everything? Or what about a case like this: class C { char[] str; int opApply(int delegate(inout char[]) dg) { for(int i = 1; i<=str.length; i++) for(int ret = dg(str[0..i])) // fails b/c slices aren't L-values return ret; } } Oh well, I guess I'll just have to find workarounds.
Jan 28 2007