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Comment by Heliodex

18 hours ago

A comment <https://github.com/LuaJIT/LuaJIT/issues/1475#issuecomment-47...> has already been made on the issue regarding the ternary operator, recommending `if x then y else z` over `x ? y : z`. This is exactly how it's done with if-then-else expressions in Luau <https://luau.org/syntax/#if-then-else-expressions>, another language compatible with Lua, and makes it a ton easier to nest (especially with elseif) and I believe still easier to read than `y if x else z`.

13 comments

Heliodex

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noelwelsh  12 hours ago

Exactly. I don't understand why people think the ternary operator is needed when you can just make `if` an expression instead of a statement. Then there is no new syntax to learn and `if` just becomes more useful.

  • aeonflux  5 hours ago

    I don't really understand where is this need to compress the logic into where small chunks comes from. In result we get single line of code which has multiple statement conditions, different paths, and it's not possible to grasp in one go.

    Other practical example why ternary is bad: Many code-coverage solutions break on ternary because they don't correctly see that one of the branches was missed in tests.

    • bruce343434  2 hours ago

      Because you can deduplicate certain parts of the logic which make the whole thing less error prone, such as

          if c
      x=1
    else
      x=2

      If I ever want to change x, or refactor this code some other way, its a more brittle process over x=c?1:2

      The ternary expression also takes up much less space so there is less of an emphasis on it, this can be a stylistic tool in a programmer's toolbox

drunken_thor  4 hours ago

I think that allowing an if statement to return a value to deal with the ternary introduces a now concept to Lua and that is that the value on the final line of a block is a return value much like Ruby. This changes the logic of the entire language more than adding a ternary. I do prefer the if statement as it allows so much more emergent behaviour, but it does have more implications to consider.

  • Heliodex  2 hours ago

    I suppose, though I feel what most people in this thread are thinking of is updating the existing if statement to also work as an expression, which does have plenty of implications (not that I think they would be bad, just more of a change to the language than the feature designers were going for) including final returns. The example I took from Luau still keeps the if statement and the if-then-else expression as separate constructs. One problem is that the statement and expression versions look very similar despite having different semantics (expression version must only contain expressions in its branches, must have an `else` case, does not have `end`).

    Of course there are differences between LuaJIT and Luau that I think influence their decisions on possible ternary expression features:

    - Luau users are disproportionately beginners to programming that I believe would find the if-then-else expression syntax easier to learn; LuaJIT developers have a larger user base of professional devs wanting to make their code faster, and they will probably be more familiar with the `x ? y : z` style since it's used in plenty of other languages.

    - Luau is a lot faster moving in its development than LuaJIT in terms of language features, the Luau team just wanted to move people to ternaries from `x and y or z` because it's easier to optimise in a normal interpreter; LuaJIT, with their JIT, I assume would be able to more easily implement optimisations for constructs like `x and y or z` despite its slight semantic differences (my assumption on why the change is being considered now rather than earlier).

mjcohen  17 hours ago

The ternary operator is easy to nest if you put each clause on a separate line. Then it looks just like nested if-then-else.