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i wouldn't have said that the ! is there because the designers want you to favour immutable rather than mutable operations. it's there for the same reason confi

i wouldn't have said that the ! is there because the designers want you to favour immutable rather than mutable operations. it's there for the same reason confirmations are there for deleting files; they want to you be sure you know what you're doing, because the immutable operation is always safe while the mutable operation is sometimes unsafe. if the ! for mutable operations weren't there, people would often be very surprised by the behaviour of reverse, sort, etc because in languages like ruby (python, etc too) they expect things to be fairly safe by default. there are plenty of cases when mutating an object is far preferable to doing the same in an immutable way for both speed, and algorithmic complexity.

steveklabnik 10y ago
Small Ruby conventions note: ! means "dangerous", not "mutable." Yeah, sometimes the kind of danger you're looking at is mutability, but it's a bit broader than that.
- tamal 10y ago
  To expand, ! means it's a more dangerous version of the method without the ![0]. A method could be dangerous, but not have a safer counterpart, and thus be named without a !. [0] https://www.ruby-forum.com/topic/176830#773946 https://www.ruby-forum.com/topic/176830#773946
- tyre 10y ago
  That's not what the ! means. Matz has said a few times that this is not the case. "Bang" methods do not necessarily mean dangerous, just different.
  - glitchdout 10y ago
    That's actually the meaning Matz gives !. http://www.rubyletter.com/blog/2017/01/31/when-to-use-ruby-bang.html http://www.rubyletter.com/blog/2017/01/31/when-to-use-ruby-b...
parenthephobia 10y ago
It's neither. It's reject! because reject already exists. Ruby isn't Scheme: a ! suffix doesn't have a simple conventional meaning. (Unlike a ? suffix.) The standard library has lots of side-effecting methods which don't come with ! suffix. On the same Array type that has reject!, there's delete, pop, push, among others. Only some of them have pure equivalents - e.g. last for pop.
- 8fGTBjZxBcHq 10y ago
  Methods in ruby only have the bang if there's another version of the method and this one might surprise you. Push and pop don't have it because they mutate the array like they do in almost every non-hardcore-functional language, so that's the expected behavior. Things like map! and reject! have them because there _is_ another version, and _this_ one might bite you. It has nothing to do with side-effects or immutability per se, that's just the most common case.
- smitherfield 10y ago
  My impression is that the convention is a ! suffix means both that 1) There's another, similar, method without the suffix. 2) The ! version has some side effect (usually mutating something or throwing an exception) that the non-! doesn't, which doesn't mean that the non-! has no side effects (`ApplicationRecord#save` and `#save!` both have side effects, but only `#save!` throws on failure). — Is there any idiomatic Ruby library where ! methods don't follow this convention?

steveklabnik 10y ago

Small Ruby conventions note: ! means "dangerous", not "mutable." Yeah, sometimes the kind of danger you're looking at is mutability, but it's a bit broader than that.

tamal 10y ago
To expand, ! means it's a more dangerous version of the method without the ![0]. A method could be dangerous, but not have a safer counterpart, and thus be named without a !. [0] https://www.ruby-forum.com/topic/176830#773946 https://www.ruby-forum.com/topic/176830#773946
tyre 10y ago
That's not what the ! means. Matz has said a few times that this is not the case. "Bang" methods do not necessarily mean dangerous, just different.
- glitchdout 10y ago
  That's actually the meaning Matz gives !. http://www.rubyletter.com/blog/2017/01/31/when-to-use-ruby-bang.html http://www.rubyletter.com/blog/2017/01/31/when-to-use-ruby-b...

parenthephobia 10y ago

It's neither. It's reject! because reject already exists. Ruby isn't Scheme: a ! suffix doesn't have a simple conventional meaning. (Unlike a ? suffix.) The standard library has lots of side-effecting methods which don't come with ! suffix. On the same Array type that has reject!, there's delete, pop, push, among others. Only some of them have pure equivalents - e.g. last for pop.

8fGTBjZxBcHq 10y ago
Methods in ruby only have the bang if there's another version of the method and this one might surprise you. Push and pop don't have it because they mutate the array like they do in almost every non-hardcore-functional language, so that's the expected behavior. Things like map! and reject! have them because there _is_ another version, and _this_ one might bite you. It has nothing to do with side-effects or immutability per se, that's just the most common case.
smitherfield 10y ago
My impression is that the convention is a ! suffix means both that 1) There's another, similar, method without the suffix. 2) The ! version has some side effect (usually mutating something or throwing an exception) that the non-! doesn't, which doesn't mean that the non-! has no side effects (`ApplicationRecord#save` and `#save!` both have side effects, but only `#save!` throws on failure). — Is there any idiomatic Ruby library where ! methods don't follow this convention?