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In STL there are many const declared member functions, without parameters,
that return a value.

There is no reason to call such functions without checking the result.

One example is std::vector::empty(). Beginners often mistake it for the
verb "to make empty" and disregard the returned boolean (hopefully it will
be called "is_empty" in STL 2.0 to avoid ambiguity).

If the nodiscard attribute was added, the compiler would be encouraged to
issue a warning when such a function is used incorrectly.

Do you think that would be a good idea?

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<div dir=3D"ltr"><div>In STL there are many const declared member functions=
, without parameters, that return a value.<br><br>There is no reason to cal=
l such functions without checking the result.<br><br>One example is std::ve=
ctor::empty(). Beginners often mistake it for the verb &quot;to make empty&=
quot; and disregard the returned boolean (hopefully it will be called &quot=
;is_empty&quot; in STL 2.0 to avoid ambiguity).<br><br>If the nodiscard att=
ribute was added, the compiler would be encouraged to issue a warning when =
such a function is used incorrectly.<br><br>Do you think that would be=C2=
=A0a good idea?</div></div>

<p></p>

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The problem here is that many newbies are not sufficiently informed that
they should compile with all warnings on, where unused return values are a
common warning if they did. How would nodiscard help with that, unless it
was made mandatory to warn about it regardless of the user's settings?

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<div dir=3D"ltr">The problem here is that many newbies are not sufficiently=
 informed that they should compile with all warnings on, where unused retur=
n values are a common warning if they did. How would nodiscard help with th=
at, unless it was made mandatory to warn about it regardless of the user&#3=
9;s settings?<br></div>

<p></p>

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This seems more like a quality-of-implementation thing. It's not like
`[[noreturn]]`, which the compiler can actually use to optimize code
better. This attribute exists solely to cause warnings to happen.

So let implementers decide when they want to issue such warnings.

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<div dir=3D"ltr">This seems more like a quality-of-implementation thing. It=
&#39;s not like `[[noreturn]]`, which the compiler can actually use to opti=
mize code better. This attribute exists solely to cause warnings to happen.=
<br><br>So let implementers decide when they want to issue such warnings.<b=
r></div>

<p></p>

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I think the warning should be enabled at a less strict warning level than
"all".

Sometimes it makes sense to ignore return values, but never with functions
such as empty().

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<div dir=3D"ltr"><div>I think the warning should be enabled at a less stric=
t warning level than &quot;all&quot;.</div><div><br></div><div>Sometimes it=
 makes sense to ignore return values, but never with=C2=A0functions such as=
 empty().=C2=A0</div></div>

<p></p>

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On Thu, Nov 17, 2016 at 5:49 PM, Nicol Bolas <jmckesson@gmail.com> wrote:

> So let implementers decide when they want to issue such warnings.
>

+1.  Especially since if the standard gets it wrong, it takes 3-6 years to
correct it (if it ever gets fixed at all).

Are these hiding real bugs?  You call functions to modify state and/or
query state.  In my experience, it's the functions that modify state
*and* return
some other state that are prime candidates (and even then, most of those
functions are correct and legal to call while ignoring their return value).
--
 Nevin ":-)" Liber  <mailto:nevin@eviloverlord.com>  +1-847-691-1404

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<div dir=3D"ltr"><div class=3D"gmail_extra">On Thu, Nov 17, 2016 at 5:49 PM=
, Nicol Bolas <span dir=3D"ltr">&lt;<a href=3D"mailto:jmckesson@gmail.com" =
target=3D"_blank">jmckesson@gmail.com</a>&gt;</span> wrote:<br><div class=
=3D"gmail_quote"><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8=
ex;border-left:1px #ccc solid;padding-left:1ex"><div dir=3D"ltr">So let imp=
lementers decide when they want to issue such warnings.</div></blockquote><=
div>=C2=A0</div></div>+1.=C2=A0 Especially since if the standard gets it wr=
ong, it takes 3-6 years to correct it (if it ever gets fixed at all).</div>=
<div class=3D"gmail_extra"><br></div><div class=3D"gmail_extra">Are these h=
iding real bugs?=C2=A0 You call functions to modify state and/or query stat=
e.=C2=A0 In my experience, it&#39;s the functions that modify state <i>and<=
/i>=C2=A0return some other state that are prime candidates (and even then, =
most of those functions are correct and legal to call while ignoring their =
return value).<br>-- <br><div class=3D"gmail_signature" data-smartmail=3D"g=
mail_signature"><div dir=3D"ltr"><div><div dir=3D"ltr"><div>=C2=A0Nevin &qu=
ot;:-)&quot; Liber=C2=A0 &lt;mailto:<a href=3D"mailto:nevin@eviloverlord.co=
m" target=3D"_blank">nevin@eviloverlord.com</a>&gt; =C2=A0+1-847-691-1404</=
div></div></div></div></div>
</div></div>

<p></p>

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Well, at least I've seen such bugs. I think implementers should consider it.

My main concern is with function names that doesn't make clear what the
function does.

"Class names are nouns, function names are verbs" is a common naming
convention.

It can be a bit confusing to introduce STL in codebases where names like
"empty" and "size" have the verb meaning.

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<div dir=3D"ltr"><div>Well, at least I&#39;ve seen such bugs. I think imple=
menters should consider it.<br><br>My main concern is with function names t=
hat doesn&#39;t make clear what the function does.<br><br>&quot;Class names=
 are nouns, function names are verbs&quot; is a common naming convention.<b=
r><br>It can be a bit confusing to introduce STL in codebases where names l=
ike &quot;empty&quot; and &quot;size&quot; have the verb meaning.</div></di=
v>

<p></p>

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On Fri, Nov 18, 2016 at 2:29 AM, <williamsson@gmail.com> wrote:

> It can be a bit confusing to introduce STL in codebases where names like
> "empty" and "size" have the verb meaning.
>
>
While some newbie might think empty() clears the container (by ignoring
that it is a const member function, but they can would think it returns the
previous emptiness state of the container, and just cast the result to
void), I cannot imagine what they believe size() with no parameters would
do.  Since you've seen these bugs, could you describe them in more detail?
--
 Nevin ":-)" Liber  <mailto:nevin@eviloverlord.com>  +1-847-691-1404

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<div dir=3D"ltr"><div class=3D"gmail_extra">On Fri, Nov 18, 2016 at 2:29 AM=
,  <span dir=3D"ltr">&lt;<a href=3D"mailto:williamsson@gmail.com" target=3D=
"_blank">williamsson@gmail.com</a>&gt;</span> wrote:<br><div class=3D"gmail=
_quote"><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border=
-left:1px #ccc solid;padding-left:1ex"><div dir=3D"ltr"><div>It can be a bi=
t confusing to introduce STL in codebases where names like &quot;empty&quot=
; and &quot;size&quot; have the verb meaning.</div></div><span class=3D"">

<p></p></span></blockquote></div><br>While some newbie might think empty() =
clears the container (by ignoring that it is a const member function, but t=
hey can would think it returns the previous emptiness state of the containe=
r, and just cast the result to void), I cannot imagine what they believe si=
ze() with no parameters would do.=C2=A0 Since you&#39;ve seen these bugs, c=
ould you describe them in more detail?<br>-- <br><div class=3D"gmail_signat=
ure" data-smartmail=3D"gmail_signature"><div dir=3D"ltr"><div><div dir=3D"l=
tr"><div>=C2=A0Nevin &quot;:-)&quot; Liber=C2=A0 &lt;mailto:<a href=3D"mail=
to:nevin@eviloverlord.com" target=3D"_blank">nevin@eviloverlord.com</a>&gt;=
 =C2=A0+1-847-691-1404</div></div></div></div></div>
</div></div>

<p></p>

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I haven't seen size() being used incorrectly, but I've seen bugs where
programmers called empty as they thought it cleared the vector. The name is
misleading.

A warning might create suspicion, but like you said we can't know for sure
if it stops them from casting to void.

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<div dir=3D"ltr"><div>I haven&#39;t=C2=A0seen size() being used incorrectly=
, but I&#39;ve seen bugs where programmers called empty as they thought it =
cleared the vector. The name is misleading.</div><div><br>A warning might c=
reate suspicion, but like you said we can&#39;t know for sure if it stops t=
hem from casting to void.</div></div>

<p></p>

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The kind of new user who would make that mistake about empty() is not going
to know that casting to void is a thing that can be done.

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<div dir=3D"ltr">The kind of new user who would make that mistake about emp=
ty() is not going to know that casting to void is a thing that can be done.=
<br></div>

<p></p>

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On 2016-11-18 03:29, williamsson@gmail.com wrote:
> "Class names are nouns, function names are verbs" is a common naming
> convention.

This is incomplete. *Imperative* functions are verbs. *Introspective*
functions may be *linking* verbs, sometimes with a noun or adjective
(e.g. `is_X`, `has_X`, `contains`), but may *also* be nouns (but more
specifically, *attributive* nouns) or adjectives alone. (Unless you're
one of those people that think everything should start with `get`.)

> It can be a bit confusing to introduce STL in codebases where names like
> "empty" and "size" have the verb meaning.

The trouble, of course, is that `empty` can be *either* a verb or an
adjective; `is_empty` - being unambiguously in the introspective
function category - would have been better.

--
Matthew

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The big problem is that all std is made without is_x  has_x, Making
is_empty() we are organizing the C++ naming notation, and if empty() will
be changed, why not all the std will go along?
Ex:
ostream::precision() -> set_precision()
ostream::fill() -> set_fill()
equal() -> is_equal()
.............

[Acidentally C++11 has a is_permutation() STL function]



Em quinta-feira, 17 de novembro de 2016 21:33:11 UTC-2, willi...@gmail.com
escreveu:
>
> In STL there are many const declared member functions, without parameters,
> that return a value.
>
> There is no reason to call such functions without checking the result.
>
> One example is std::vector::empty(). Beginners often mistake it for the
> verb "to make empty" and disregard the returned boolean (hopefully it will
> be called "is_empty" in STL 2.0 to avoid ambiguity).
>
> If the nodiscard attribute was added, the compiler would be encouraged to
> issue a warning when such a function is used incorrectly.
>
> Do you think that would be a good idea?
>

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<div dir=3D"ltr">The big problem is that all std is made without is_x =C2=
=A0has_x, Making is_empty() we are organizing the C++ naming notation, and =
if empty() will be changed, why not all the std will go along?<div>Ex:</div=
><div>ostream::precision() -&gt; set_precision()</div><div>ostream::fill() =
-&gt; set_fill()<br></div><div>equal() -&gt; is_equal()</div><div>.........=
....</div><div><br></div><div>[Acidentally C++11 has a is_permutation() STL =
function]</div><div><br></div><div><br><br>Em quinta-feira, 17 de novembro =
de 2016 21:33:11 UTC-2, willi...@gmail.com  escreveu:<blockquote class=3D"g=
mail_quote" style=3D"margin: 0;margin-left: 0.8ex;border-left: 1px #ccc sol=
id;padding-left: 1ex;"><div dir=3D"ltr"><div>In STL there are many const de=
clared member functions, without parameters, that return a value.<br><br>Th=
ere is no reason to call such functions without checking the result.<br><br=
>One example is std::vector::empty(). Beginners often mistake it for the ve=
rb &quot;to make empty&quot; and disregard the returned boolean (hopefully =
it will be called &quot;is_empty&quot; in STL 2.0 to avoid ambiguity).<br><=
br>If the nodiscard attribute was added, the compiler would be encouraged t=
o issue a warning when such a function is used incorrectly.<br><br>Do you t=
hink that would be=C2=A0a good idea?</div></div></blockquote></div></div>

<p></p>

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