Forgetting to do


import std.functional: binaryFun;


before trying to compile

bool skipOverSafe(alias pred = "a == b", R1, R2)(ref R1 r1, R2 r2)
    @safe pure if (is(typeof(binaryFun!pred(r1.front, r2.front))))
{
    return r1.length >= r2.length && skipOver!pred(r1, r2); // TODO: Can we prevent usage of .length?
}

unittest
{
    auto s1 = "Hello world";
    assert(!skipOverSafe(s1, "Ha"));
}


gives no clue about the missing import in the diagnostics.

Is this a other/newer preferred way to describe the template restriction, using for example __traits(compiles, ...)? Is

is(typeof(...

the fastest way to do this?

BTW: Is there a way to prevent the calls to r1.length and r2.length in this case?

On Monday, 1 September 2014 at 22:46:52 UTC, Nordlöw wrote:
> Is this a other/newer preferred way to describe the template restriction, using for example __traits(compiles, ...)? Is
>
> is(typeof(...

AFAIK, those produce the same results 99% of the time. The only cases where they differ are borderline buggy.

> the fastest way to do this?

Are you talking about constraints, or implementation of safeSkipOver?

> BTW: Is there a way to prevent the calls to r1.length and r2.length in this case?

Hum... Are you writing this function because skipOver will actually fail? AFAIK, it shouldn't. We should fix skipOver...

On Monday, 1 September 2014 at 22:46:52 UTC, Nordlöw wrote:
> BTW: Is there a way to prevent the calls to r1.length and r2.length in this case?

Also, this assumes your ranges have front at all. AFAIK, skipOver operates on forward ranges. Related: Your condition could fail if R1/R2 are strings of un-matching widths.

On Tuesday, 2 September 2014 at 10:22:49 UTC, monarch_dodra wrote:
>> the fastest way to do this?
>
> Are you talking about constraints, or implementation of safeSkipOver?

The constraint.

> Hum... Are you writing this function because skipOver will actually fail? AFAIK, it shouldn't. We should fix skipOver...

Yes, I'm writing this wrapper because call to r.front in

bool skipOver(alias pred = "a == b", R, E)(ref R r, E e)
if (is(typeof(binaryFun!pred(r.front, e))))
{
    if (!binaryFun!pred(r.front, e))
        return false;
    r.popFront();
    return true;
}

fails when r is empty.

It believe it should be

    if (r.empty || !binaryFun!pred(r.front, e))

right? Should I do a PR?

On Tuesday, 2 September 2014 at 11:41:51 UTC, Nordlöw wrote:
> On Tuesday, 2 September 2014 at 10:22:49 UTC, monarch_dodra wrote:
>>> the fastest way to do this?
>>
>> Are you talking about constraints, or implementation of safeSkipOver?
>
> The constraint.

In that case, I'm not sure what you mean by "fastest" in the context of "constraints", which are compile-time.

>> Hum... Are you writing this function because skipOver will actually fail? AFAIK, it shouldn't. We should fix skipOver...
>
> Yes, I'm writing this wrapper because call to r.front in
>
> bool skipOver(alias pred = "a == b", R, E)(ref R r, E e)
> if (is(typeof(binaryFun!pred(r.front, e))))
> {
>     if (!binaryFun!pred(r.front, e))
>         return false;
>     r.popFront();
>     return true;
> }
>
> fails when r is empty.
>
> It believe it should be
>
>     if (r.empty || !binaryFun!pred(r.front, e))
>
> right? Should I do a PR?

I think so yes. That's the "R/E" version though. Is the "R/R" version also subject to this issue?

On Tuesday, 2 September 2014 at 12:14:01 UTC, monarch_dodra wrote:
> In that case, I'm not sure what you mean by "fastest" in the context of "constraints", which are compile-time.

With performance I mean compilation speed.

> I think so yes. That's the "R/E" version though. Is the "R/R" version also subject to this issue?

No, it's only the R/E that lacks emptyness check.

PR: https://github.com/D-Programming-Language/phobos/pull/2481