Break and Continue:
In a talk about Scala, Martin Odersky gave 3 reasons not to include break or continue on slide 22:
- They are a bit imperative; better use many smaller functions.
- Issues how to interact with closures.
- They are not needed!
And he then says, "We can support them purely in the libraries." On slide 23, he gives code that implements break
. Although I don't quite know Scala well enough to be certain, it looks like the short snippet on that slide is all that's needed to implement break
, and that continue
could be implemented in code that is similarly short.
Being able to implement stuff like this in libraries simplifies the core language.
In 'Programming in Scala, Second Edition', by Martin Odersky, Lex Spoon, and Bill Venners, the following explanation is given:
You may have noticed that there has been no mention of break
or continue
. Scala leaves out these commands because they do not mesh well with function literals... It is clear what continue
means inside a while
loop, but what would it mean inside a function literal? ... There are many ways to program without break
and continue
, and if you take advantage of function literals, those alternatives can often be shorter than the original code.
Return:
Returns could be considered a bit imperative in style, since return is a verb, a command to do something. But they can also be seen in a purely functional/declarative way: they define what the return value of the function is (even if, in a function with multiple returns, they only each give a partial definition).
In the same book, they say the following about return
:
In the absence of any explicit return
statement, a Scala method returns the last value computed by the method. The recommended style for methods is in fact to avoid having explicit, and especially multiple, return
statements. Instead, think of each method as an expression that yields one value, which is returned.
Methods end and return a value, even if a return
statement isn't used, so there can be no issues with closures, since otherwise closures wouldn't work period.
There can also be no problem meshing well with function literals, since the function has to return a value anyway.
break
andcontinue
need some additional cleanup machinery. OTOHreturn
is a way to orderly terminate a function, and any cleanup machinery is already there anyway. – 9000 Oct 13 '14 at 15:14breakable { for { break; } }
but an afterthought, and likely far from efficient. – Joop Eggen Oct 13 '14 at 15:17break
andcontinue
is contained in your question and in the link in your question. The question forreturn
is exactly what the question I linked was about, and was answered, at least in the top-voted, accepted answer. If the two answers put together don't answer your question, maybe you could edit the question to clarify it. – Michael Shaw Oct 13 '14 at 22:36