5 ms·

C++: terser (shorter) lambda == SHORTY (ab-use?)

67 points by signa11 2y ago

porridgeraisin 2y ago
That's horrifying
- mbel 2y ago
  To be honest the implementation looks surprisingly readable… at least compared to other horrors like the standard library implementation. While there are some new rules regarding arguments naming, the new syntax doesn’t feel more complex than the default lambda syntax. So all in all I would say the most horrifying thing here is the fact that the language allows such extensions in the first place ;)
  - ratmeadow 2y ago
    Once you strip out all the helper code for tuples and args, it's really not the worst. Made sense to me on the first read. Sensible naming and not that much metaprogramming indirection going on, thank god. Or maybe I am too brainwashed by C++ at this point.
hsfzxjy 2y ago
Looks cursed to me. But TIL dollar sign $ is also valid character for identifiers.
- tempodox 2y ago
  > $ is also valid character for identifiers. Has been like that in C since forever.
  - skullt 2y ago
    It's a common extension but it's not standard. Both C23 and C++23 only allow identifiers to start with a Unicode XID_START character, which excludes $. And with older standards, it was just Latin letters, the underscore, and explicit \u escapes. If you look in the project's pedantic.cmake, you'll find a add_c_and_cxx_compile_options("-Wno-dollar-in-identifier-extension") just to suppress warnings about this.
    - deleted 2y ago
      [deleted]
  - ksherlock 2y ago
    VMS used $ - eg sts = sys$getjpiw(0, 0, 0, &jpi_itm_lst, 0, 0, 0); if ((sts & STS$M_SEVERITY) != STS$K_SUCCESS) That might be why GCC originally included $ support.
pwdisswordfishz 2y ago
Isn’t this basically the obsolete Boost.Lambda?
- beojan 2y ago
  It's like Boost Lambda2 or Boost HOF. Boost Hana also has a similar feature. This seems to be more fully featured than all of those though. Maybe some could be ported over to Lambda2.
foxhill 2y ago
huh. very cute. in the past, i had an idea for terser lambda syntax, similar to C#'s expression body functions - which i did end up implementing in clang: auto sum = [](auto a, auto b): a+b; but this is something else. i didn't think i'd like it at first, but actually i think i might be coming around to it. the.. dollar syntax is regrettable, although it's not a show stopper.
notpushkin 2y ago
Neat. Reminds me of https://github.com/dry-python/lambdas https://github.com/dry-python/lambdas
- andrepd 2y ago
  I've always thought this should be first-class syntax in any language with lambdas
szundi 2y ago
[dead]
tempodox 2y ago
As if C++ didn't have enough of “black magic” already, there's another layer of that. Just in case you find error messages involving template applications still too readable.
- fouronnes3 2y ago
  Little reminder that there once was a "C++ error message competition" [0] where your score was measured as "the size of the error message divided by the size of the source code". The winning entry had a score of 5.9 billion. [0] https://tgceec.tumblr.com/post/74534916370/results-of-the-grand-c-error-explosion?is_related_post=1 https://tgceec.tumblr.com/post/74534916370/results-of-the-gr...
  - tempodox 2y ago
    2014 but still hilarious, although the winner had nothing to do with templates. From one of the entries: > Extra credit for using Perl, which is the only language less readable than C++ templates.
nialv7 2y ago
Not really a new idea. These are expression templates: https://en.wikipedia.org/wiki/Expression_templates https://en.wikipedia.org/wiki/Expression_templates
GrantMoyer 2y ago
Another idea in this vein, but with a surprisingly straightforward implementation (27 lines): https://github.com/GrantMoyer/lambda_hpp https://github.com/GrantMoyer/lambda_hpp I started out trying to write something like the OP, but changed direction when I convinced myself there would have been no sane way to implement member call syntax. I honestly can't decide if it's cursed or genuinely useful (minus the unicode name, that's cursed).
pjmlp 2y ago
I fail to see the benefit from the lens of C++23.
curtisszmania 2y ago
[dead]
gnulinux 2y ago
I'm sorry I know this is horrific but I still love it. This looks like a better version of Boost Lambda2. I would potentially maybe replace `$` with `_` before using this (which should be easy as a layer) like Boost::Lambda2 but otherwise I'm excited to use it. Not that I would use anything like this in production, but it looks too fun not to play around with.
ratmeadow 2y ago
Pretty cool. I was wondering what kind of arcane magic they used to get $xxx working, since $ is not a standard identifier char... then I realised they straight up define $arg, $call, etc as constants (makes a lot of sense). And $ really is not an identifier char by the Standard, but evidently some compilers accept it.

67 points by signa11 2y ago

porridgeraisin 2y ago

That's horrifying

mbel 2y ago
To be honest the implementation looks surprisingly readable… at least compared to other horrors like the standard library implementation. While there are some new rules regarding arguments naming, the new syntax doesn’t feel more complex than the default lambda syntax. So all in all I would say the most horrifying thing here is the fact that the language allows such extensions in the first place ;)
- ratmeadow 2y ago
  Once you strip out all the helper code for tuples and args, it's really not the worst. Made sense to me on the first read. Sensible naming and not that much metaprogramming indirection going on, thank god. Or maybe I am too brainwashed by C++ at this point.

hsfzxjy 2y ago

Looks cursed to me. But TIL dollar sign $ is also valid character for identifiers.

tempodox 2y ago
> $ is also valid character for identifiers. Has been like that in C since forever.
- skullt 2y ago
  It's a common extension but it's not standard. Both C23 and C++23 only allow identifiers to start with a Unicode XID_START character, which excludes $. And with older standards, it was just Latin letters, the underscore, and explicit \u escapes. If you look in the project's pedantic.cmake, you'll find a add_c_and_cxx_compile_options("-Wno-dollar-in-identifier-extension") just to suppress warnings about this.
  - deleted 2y ago
    [deleted]
- ksherlock 2y ago
  VMS used $ - eg sts = sys$getjpiw(0, 0, 0, &jpi_itm_lst, 0, 0, 0); if ((sts & STS$M_SEVERITY) != STS$K_SUCCESS) That might be why GCC originally included $ support.

pwdisswordfishz 2y ago

Isn’t this basically the obsolete Boost.Lambda?

beojan 2y ago
It's like Boost Lambda2 or Boost HOF. Boost Hana also has a similar feature. This seems to be more fully featured than all of those though. Maybe some could be ported over to Lambda2.

foxhill 2y ago

huh. very cute. in the past, i had an idea for terser lambda syntax, similar to C#'s expression body functions - which i did end up implementing in clang: auto sum = [](auto a, auto b): a+b; but this is something else. i didn't think i'd like it at first, but actually i think i might be coming around to it. the.. dollar syntax is regrettable, although it's not a show stopper.

notpushkin 2y ago

Neat. Reminds me of https://github.com/dry-python/lambdas https://github.com/dry-python/lambdas

andrepd 2y ago
I've always thought this should be first-class syntax in any language with lambdas

szundi 2y ago

[dead]

tempodox 2y ago

As if C++ didn't have enough of “black magic” already, there's another layer of that. Just in case you find error messages involving template applications still too readable.

fouronnes3 2y ago
Little reminder that there once was a "C++ error message competition" [0] where your score was measured as "the size of the error message divided by the size of the source code". The winning entry had a score of 5.9 billion. [0] https://tgceec.tumblr.com/post/74534916370/results-of-the-grand-c-error-explosion?is_related_post=1 https://tgceec.tumblr.com/post/74534916370/results-of-the-gr...
- tempodox 2y ago
  2014 but still hilarious, although the winner had nothing to do with templates. From one of the entries: > Extra credit for using Perl, which is the only language less readable than C++ templates.

nialv7 2y ago

Not really a new idea. These are expression templates: https://en.wikipedia.org/wiki/Expression_templates https://en.wikipedia.org/wiki/Expression_templates

GrantMoyer 2y ago

Another idea in this vein, but with a surprisingly straightforward implementation (27 lines): https://github.com/GrantMoyer/lambda_hpp https://github.com/GrantMoyer/lambda_hpp I started out trying to write something like the OP, but changed direction when I convinced myself there would have been no sane way to implement member call syntax. I honestly can't decide if it's cursed or genuinely useful (minus the unicode name, that's cursed).

pjmlp 2y ago

I fail to see the benefit from the lens of C++23.

curtisszmania 2y ago

[dead]

gnulinux 2y ago

I'm sorry I know this is horrific but I still love it. This looks like a better version of Boost Lambda2. I would potentially maybe replace `$` with `_` before using this (which should be easy as a layer) like Boost::Lambda2 but otherwise I'm excited to use it. Not that I would use anything like this in production, but it looks too fun not to play around with.

ratmeadow 2y ago

Pretty cool. I was wondering what kind of arcane magic they used to get $xxx working, since $ is not a standard identifier char... then I realised they straight up define $arg, $call, etc as constants (makes a lot of sense). And $ really is not an identifier char by the Standard, but evidently some compilers accept it.