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C++20 Improved the For-Loop Syntax

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Re: C++20 Improved the For-Loop Syntax

#21

Post by zeroq »

tcfhgj wrote: post #12
petilon wrote: post #5

Earlier quoted context omitted.

C++ is probably the only language that needs a strong style guide, to define a subset you are allowed to use in the project. Linus Torwalds famously said that subset is zero. You're not allowed to use C++ in Linux, a wise move. Here's Google's: https://google.github.io/styleguide/cppguide.html Search for "do not use" and you'll find plenty of hits.

> C++ is probably the only language that needs a strong style guide, here you go: https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines

Good Lord.

Reminds me of Good Parts, Bad Parts meme of JS.

Re: C++20 Improved the For-Loop Syntax

#22

Post by [deleted] »

Gualdrapo wrote: post #7
WCSTombs wrote: post #3

The C++20 version is still clearly inferior to the Python and Lua examples because you still have to manually increment the counter in the loop body. IMO the sibling comment by HarHarVeryFunny has a much better C++ equivalent for this idiom, even if it's slightly more verbose.

> you still have to manually increment the counter in the loop body It doesn't look like that to me, the ++i thing seems to be just to start printing the array from 1 (I don't know how things are in Python nowadays but I know in Lua arrays start at 1, so there's no need for something like this in there), the value of i is still increasing without telling it explicitly to do so

[deleted]

Re: C++20 Improved the For-Loop Syntax

#24

Post by arikrahman »

HarHarVeryFunny wrote: post #2

C++20 also has an enumerate() generator, so if you like the python syntax you can just do: for (auto [i,v] : std::views::enumerate(vec)) std::cout FWIW C++23 also has a python-like print and println: std::println("{}: {}", i, v);

This is the way I've been doing it and with less hiccups.

Re: C++20 Improved the For-Loop Syntax

#25

Post by lioeters »

dvt wrote: post #15

I am so happy I haven't written a line of C++ in like 15 years. Absolutely disgusting language. Every time I look up one of their new standards, I'm like how does anyone keep all of this in their head (usually on top of stuff like boost, etc.)? No wonder LLMs are a thing.

C++ is a decades-long mistake that spawned other misguided directions in the entire software industry. We're still trying to undo many of the bad ideas, but I'm afraid even Rust has too much of C++ in it, not only in terms of syntax but mentality and culture. LLMs are making things worse by automatically generating code in such bloated languages, where people have less need to even look at the horrific spaghetti inside. The whole thing needs to be reconsidered from the ground up, from first principles, by actual creative thinking human beings with lessons of hindsight.

> Gall's Law: A complex system that works is invariably found to have evolved from a simple system that worked. A complex system designed from scratch never works and cannot be patched up to make it work. You have to start over with a working simple system.

Re: C++20 Improved the For-Loop Syntax

#26

Post by kazinator » 

  1> (mapdo (op put-line `@1: @2`) '#"how now brown cow" 0)
  how: 0
  now: 1
  brown: 2
  cow: 3
  nil
mapdo: a mapping function for side effects of calling the function, not calculating a result, like map does.

op: produce a lambda expression out of an expression in which @1, @2, ... explicitly indicate the insertion of positional arguments, which are implicitly collected and become the parameter list of the lambda.

`...`: quasistring syntax: supports @ notations for interpolating. The @1, @2 elements of op do not require a double @@ inside a quasistring.

put-line: ordinary function to put a string to a stream (standard output by default) followed by newline. The lambda generated by op contains a (put-line ...) expression as its body, with @1 and @2 transformed into references to to generated, unique parameter names.

#"...": string list literal: contents are broken on whitespace and denote a list of strings #"foo bar" -> ("foo" "bar"). Requires ' quote in front to be quoted literally, and not evaluated as a compound expression applying the argument "bar" to the operator "foo". Yes, there is a #`...` quasi string list for templating over this.

nil: the value returned by mapdo after the side effects, printed by the REPL, not part of the output.

0: ordinary integer zero. But endowed with the power of being iterable. Where an iterable thing is required, 0 denotes the whole numbers 0, 1, 2, ... Similarly, 42 denotes 42, 43, ...

These are some of the ingredients produced by my one-member research programme into nicer Lisp coding.

  2> (map (ret `@1: @2`) '#"how now brown cow" 0)
  ("how: 0" "now: 1" "brown: 2" "cow: 3")
map: take tuples by iterating over argument iterables in parallel, pass them to a function to project each tuple to a value, then return a list of values.

ret: cousin of op built on the same framework as op. Used for turning an expression into a lambda, when the expression isn't a compound form with an obvious operator. To turn (foo bar) into a lamdbda with op we use (op foo bar). But what if we have a simple variable x and want (lambda () x)? (op x) is not right, it means (lambda () (x)). (ret x) provides the sugar. Here, it lets us spin up a two-argument function that evaluates a quasistring.

Re: C++20 Improved the For-Loop Syntax

#27

Post by WalterBright »

WalterBright wrote: post #16

C++ should copy D's elegance: import std.stdio; string[9] vec = [ "the", "quick", "brown", "fox", "jumped", "over", "the", "lazy", "dog" ]; void main() { foreach (i, s; vec) writeln(i, ": ", s); }

Although D is a strongly typed language, it is very good at type inference. The `s` is inferred as `string`, and `i` as `size_t`.

Re: C++20 Improved the For-Loop Syntax

#28

Post by grg0 »

UncleOxidant wrote: post #23

Reading this, I really can't make much sense of it: for (int i=0; auto&& it: vec) cout It's certainly not obvious what's going on there at a glance. This is at least a bit more pythonic: for (auto [i, it] : std::views::enumerate(vec)) { std::cout

It's probably easier to understand if you read about the "if statement with initializer" linked from the post: https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p03...

Re: C++20 Improved the For-Loop Syntax

#29

Post by Maxatar »

HarHarVeryFunny wrote: post #2

C++20 also has an enumerate() generator, so if you like the python syntax you can just do: for (auto [i,v] : std::views::enumerate(vec)) std::cout FWIW C++23 also has a python-like print and println: std::println("{}: {}", i, v);

std::views::enumerate is a C++23 feature, not C++20.
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