Comment by caspper69
2 days ago
After all the Ada threads last week, I read their pdf @ Adacore's site (the Ada for Java/C++ Programmers version), and there were a lot of surprises.
A few that I found: logical operators do not short-circuit (so both sides of an or will execute even if the left side is true); it has two types of subprograms (subroutines and functions; the former returns no value while the latter returns a value); and you can't fall through on the Ada equivalent of a switch statement (select..case).
There are a few other oddities in there; no multiple inheritance (but it offers interfaces, so this type of design could just use composition).
I only perused the SPARK pdf (sorry, the first was 75 pages; I wasn't reading another 150), but it seemed to have several restrictions on working with bare memory.
On the plus side, Ada has explicit invariants that must be true on function entry & exit (can be violated within), pre- and post- conditions for subprograms, which can catch problems during the editing phase, and it offers sum types and product types.
Another downside is it's wordy. I won't go so far as to say verbose, but compared to a language like Rust, or even the C-like languages, there's not much shorthand.
It has a lot of the features we consider modern, but it doesn't look modern.
> logical operators do not short-circuit (so both sides of an or will execute even if the left side is true)
There are two syntaxes: `and` which doesn't short circuit, and `and then` which does. Ditto for `or` and `or else`.
Interestingly Rust uses the same convention for some methods: Option has "and_then", "or_else", and also a distinction between "unwrap_or" and "unwrap_or_else".
Coincidentally, this is the same as C and C++: you have & and && and then you have | and ||. We think of & and | as something that's only useful for bit twiddling, but when you apply them to boolean values, the semantics are exactly that of a non-short-circuiting boolean operator.
Thanks for the heads up.
> you can't fall through on the Ada equivalent of a switch statement (select..case).
C is actually more of an odd one here, and the fallthrough semantics is basically a side effect of it being a glorified computed goto (with "case" being literally labels, hence making things like Duff's device a possibility). Coincidentally, this is why it's called "switch", too - the name goes back all the way to the corresponding Algol-60 construct.