Thread

C++ Insights – See your source code with the eyes of a Compiler

172 points · 36 comments · rramadass

StilesCrisis · 1791036041 · focus · HN ↗
I wish the readme example showed a lambda capture. Now that's where compiler magic REALLY shows up.
1. sltkr · 1791059716 · focus · HN ↗
  C++ lambdas are just structs that overload operator(); once you realize that they become a lot less mysterious. But it's a great example of how this tool is useful to learn about those things (of course you could also read the C++ standard but who has time for that?)
  Here's an example: <a href="https://cppinsights.io/s/f04b6896" rel="nofollow">https://cppinsights.io/s/f04b6896
  (That also shows how C++'s range-based for-loops work, which is similarly some syntactic suger for a fairly mundane for-loop, but details are interesting: unlike a typical for-loop, the loop variable is declared inside the loop body.)
  1. Someone · 1791093439 · focus · HN ↗
    > That also shows how C++'s range-based for-loops work, which is similarly some syntactic suger for a fairly mundane for-loop, but details are interesting: unlike a typical for-loop, the loop variable is declared inside the loop body
    That’s not true in C++, is it? There, this does not compile
    for(int i = 0; i < 3; ++i) {} i = i + 1;
    (<a href="https://cppinsights.io/s/26405687" rel="nofollow">https://cppinsights.io/s/26405687: error: use of undeclared identifier 'i')
    <a href="https://en.cppreference.com/cpp/language/for" rel="nofollow">https://en.cppreference.com/cpp/language/for:
    “A for statement equivalent to:
    { init-statement while ( condition ) { statement expression ; } }
    Except that […]”
    and
    “While in C names declared in the scope of init-statement and condition can be shadowed in the scope of statement, it is forbidden in C++:
    for (int i = 0;;) { long i = 1; // valid C, invalid C++ // ... }
    “

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