[ruby-core:102219] [Ruby master Feature#17576] Partial Functions (procs, lambdas)
From:
matz@...
Date:
2021-01-23 14:52:15 UTC
List:
ruby-core #102219
Issue #17576 has been updated by matz (Yukihiro Matsumoto).
Is there any real-world use-case? I don't see any of them.
Besides that, proposed syntax does not work well with normal blocks.
Matz.
----------------------------------------
Feature #17576: Partial Functions (procs, lambdas)
https://bugs.ruby-lang.org/issues/17576#change-90067
* Author: temabolshakov (Tema Bolshakov)
* Status: Open
* Priority: Normal
----------------------------------------
We already have pattern matching and functions. Let's combine them and introduce a "partial procs" as first-class citizens.
What are partial procs? This is a function that works on a subset of arguments. The partial proc's main advantage is that a caller may decide in advance if this proc can accept an argument or not and do something different rather than calling it.
That's how it may look like:
```ruby
partial_proc = proc do |arg|
in x if x.odd?
"#{x} is odd"
end
```
One can check if a proc is defined on the argument
```ruby
partial_proc.defined?(42) #=> false
partial_proc.defined?(41) #=> true
```
You can call such a partial proc and it raises an error when it's not defined on this argument:
```ruby
partial_proc.call(42) #=> raises NoMatchingPatternError (42)
partial_proc.call(41) #=> 41 is odd
```
And finally, we can call or fallback to a default value:
```ruby
partial_proc.call_or_else(42) { "fallback value" } #=> 'fallback value'
partial_proc.call_or_else(41) { "fallback value" } #=> 41 is odd
```
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