Re: Using gperf to allow switch-case over strings (in c++17)

[Viktor Engelmann]

Hello Bruno,
> 1) Since 'constexpr' is a built-in keyword in C++, why does --language=C++
> not imply --constexpr in the first place? In other words, as a user I
> would like the generated code to be optimal without any additional
> command-line options.
I did it this way because I didn't want to change the behavior on
existing projects. Apart from that, I agree with your reasoning.

In the Qt Framework, things like this would be solved with a
preprocessor variable like Q_CONSTEXPR that would be
defined to constexpr or nothing at the start of the file.
> If you compile with option -S, you will see that in the functions
> Perfect_Hash::hash and Perfect_Hash::in_word_set the arrays are
> initialized *at every invocation*.
>
> I understand that this is because [1] specifies that
>    "the function body must not contain:
>     ... a definition of a variable of static ... storage duration"
correct.
> But it is a performance killer! gperf is meant to generate fast code,
> and one of the necessary requirements is that the arrays are prepared
> once only (and preferrably in read-only storage).

I agree. I worried about this, but hadn't checked it so far.

Without adding it to gperf sources yet, I manually made the tables
static constexpr class-members (see attachment test.cpp). I'm not
sure I understand the assembler code (-S) correctly, but I think
this should solve the issue.
@Bruno: What do you say about this version?

Kind regards

Viktor

test.cpp
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