4 ms·

The if expression is not a persuasive example. C/Java/Algol/etc all have it as well. x = something ? foo() : bar();

• coderzach 10y ago
  I see two issues with the ternary operator. One, the syntax is much less readable, and two, the consequent and alternate are both single expressions, so you can't do something like: x = if(something) { a = foo(); baz(a); } else { b = bar(); baz(b); }
  • heywire 10y ago
    I've always read ternary statements to myself as a question. some_condition ? this : that some_condition? then this, otherwise that Typing this, I realize how hard it is to explain without speaking it :)
    • lawpoop 10y ago
      Is the color red? If so, this; otherwise, that. It's a little tricky, because in the above, the `if` keyword appears after the question mark. Is the color red? Yes-- this: no-- that. Trying to make a parsimonious English sentence while maintaining the syntax elements : P
    • kbutler 10y ago
      > some_condition ? this : that Just read it as: IF some_condition THEN this ELSE that
  • junke 10y ago
    You compute baz in both branches, you can refactor. x = baz(if (something) foo() else bar())
  • tacostakohashi 10y ago
    If you insist on the assignments: x = something ? ((a=foo()), baz(a)) : ((b = bar()), baz(b)); Otherwise: x = something ? baz(foo()) : baz(bar());
    • vertex-four 10y ago
      a and b have to be defined before the statement containing the terniary expression here. And the point is that you can embed arbitrary multi-statement logic in your if expressions in Rust in the same way you'd do it anywhere else.
  • kazinator 10y ago
    It should work in GNU C: x = (something) ? ({ a = foo(); baz(a) }) : ({ b = bar(); baz(b); }); However, since all your forms are actually expression statements, we can happily just use the ISO C comma operator: x = (something) ? (a = foo(), baz(a)) : (b = bar(); baz(b)); If C provided operators for iteration, selection and for binding some variables over a scope (that scope consisting of an expression), everything would be cool. E.g. fantasy while loop: x = (< y 0) ?? y++ : y; // evaluate y++ while (< y 0), then yield y. Variable binding: x = let (int x = 3, double y = 3.0) : (x++, x*y); The problem is that some things can only be done with statements. The ternary operator is not actually lacking anything; with the comma operator, multiple expressions can be evaluated. What's lacking is the vocabulary of what those expressions can do.
• vertex-four 10y ago
  The difference is that C/Java/Algol have different syntaxes for things-as-expressions and things-as-statements, and you can't put blocks in the things-as-expressions. In Rust, blocks are also expressions and so have a result (the result of the last expression in the block), so your expressions inside the if can be as complex as you like. Since functions also have a block, and the return value of the function is the result of the block, this is much more consistent.
  • kazinator 10y ago
    In GNU C, you can use a brace-enclosed statement block as an expression. Funny story; years before I became a C programmer, and at a time when I didn't yet study ISO C properly, I discovered and used this extension naturally. I wanted to evaluate some statements where only an expression could be used so I thought, gee, come on, can't you just put parens around it to turn it into an expression and get the value of the last expression as a return value? I tried that and it worked. And of course, if it works it's good (standards? what are those?) Then I tried using the code with a different C compiler; oops! Anyway, this GNU C feature doesn't have as much of an impact as you might think.