meaning of ? in a function?

[António Ramos]

Hello simple question for sure 

what is the meaning of the ? in 

def  aaa?()

regards

António

[Peter Hamilton]

It has no meaning syntactically. It's just part of the function name. It is however a convention (especially common in Ruby) meaning "this function returns a boolean value".

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[Louis Pilfold]

Hi

The convention is to end a function name with a ? if it returns a
boolean value. Otherwise it has no specific meaning.

Cheers,
Louis

[António Ramos]

Got it!

thank you

2016-08-21 20:08 GMT+01:00 Louis Pilfold <lo...@lpil.uk>:

Hi

The convention is to end a function name with a ? if it returns a
boolean value. Otherwise it has no specific meaning.

Cheers,
Louis

On 21 August 2016 at 18:36, António Ramos <ramst...@gmail.com> wrote:
> Hello simple question for sure
>
> what is the meaning of the ? in
>
> def  aaa?()
>
> regards
> António
>

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[Elliot Crosby-McCullough]

Follow-up question; there's debate in Ruby as to whether methods ending in `?` are supposed to return actual booleans or just "truthy" and "falsy" values.

Is there a similar debate in Elixir or has it been more strictly defined?

On 21 August 2016 at 19:08, Peter Hamilton <petergh...@gmail.com> wrote:

It has no meaning syntactically. It's just part of the function name. It is however a convention (especially common in Ruby) meaning "this function returns a boolean value".

On Sun, Aug 21, 2016, 10:37 AM António Ramos <ramst...@gmail.com> wrote:

Hello simple question for sure 

what is the meaning of the ? in 

def  aaa?()

regards

António

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[Michał Muskała]

> On 24 Aug 2016, at 15:24, Elliot Crosby-McCullough <elli...@gmail.com> wrote:
>
> Follow-up question; there's debate in Ruby as to whether methods ending in `?` are supposed to return actual booleans or just "truthy" and "falsy" values.
>
> Is there a similar debate in Elixir or has it been more strictly defined?

I've heard José state, that if it were possible, it would be an error for a ? function to return a non-boolean. I am equally of conviction that only strictly boolean values make sense in this context.

Michał.

[Martin Svalin]

I think there's a stronger argument to be made for literal true / false, not just truthy / falsy in Elixir than Ruby.

In Ruby, the return value might be used in an if-condition. Semantically, it shouldn't matter if the value is literal true or simply truthy. Something like `if method? == true` would be considered bad code.

In Elixir, you might also use the value in pattern matching. Matching on literal `true` would be considered completely reasonable. Example:

    def entrypoint(data), do: handle(data, valid?(data))

    def handle(data, true), do: something(data)

    def handle(data, false), do: something_else(data)

Returning truthy / falsy values would hobble this sort of pattern matching. It would be even worse if I only did a literal match on false, and ignored the in the true case, which would then be run for the falsy value nil.

Another consideration is that a truthy value could potentially be large, and could then be sent off in a message to another process in the expectation that it's small.

So please, return literal true / false from your predicate functions.

- Martin

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[Elliot Crosby-McCullough]

I'm in the literal camp even in Ruby, but it's good to see some less debateable reasoning for it in Elixir, thanks.

On 24 August 2016 at 15:05, Martin Svalin <martin...@gmail.com> wrote:

I think there's a stronger argument to be made for literal true / false, not just truthy / falsy in Elixir than Ruby.

In Ruby, the return value might be used in an if-condition. Semantically, it shouldn't matter if the value is literal true or simply truthy. Something like `if method? == true` would be considered bad code.

In Elixir, you might also use the value in pattern matching. Matching on literal `true` would be considered completely reasonable. Example:

    def entrypoint(data), do: handle(data, valid?(data))

    def handle(data, true), do: something(data)

    def handle(data, false), do: something_else(data)

Returning truthy / falsy values would hobble this sort of pattern matching. It would be even worse if I only did a literal match on false, and ignored the in the true case, which would then be run for the falsy value nil.

Another consideration is that a truthy value could potentially be large, and could then be sent off in a message to another process in the expectation that it's small.

So please, return literal true / false from your predicate functions.

- Martin

ons 24 aug. 2016 kl 15:28 skrev Michał Muskała <mic...@muskala.eu>:

> On 24 Aug 2016, at 15:24, Elliot Crosby-McCullough <elli...@gmail.com> wrote:
>
> Follow-up question; there's debate in Ruby as to whether methods ending in `?` are supposed to return actual booleans or just "truthy" and "falsy" values.
>
> Is there a similar debate in Elixir or has it been more strictly defined?

I've heard José state, that if it were possible, it would be an error for a ? function to return a non-boolean. I am equally of conviction that only strictly boolean values make sense in this context.

Michał.

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[webengi...@gmail.com]

See docs also http://elixir-lang.org/docs/master/elixir/naming-conventions.html#trailing-question-mark-foo.

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Max