[ruby-core:119883] [Ruby master Feature#20885] String#gsub?

[ruby-core:119883] [Ruby master Feature#20885] String#gsub?

[Dan0042 (Daniel DeLorme) via ruby-core]

Issue #20885 has been reported by Dan0042 (Daniel DeLorme).

----------------------------------------
Feature #20885: String#gsub?
https://bugs.ruby-lang.org/issues/20885

* Author: Dan0042 (Daniel DeLorme)
* Status: Open
----------------------------------------
I would like a variation of sub/gsub that returns a new string if there is a match, or nil otherwise.

This can be currently done with `str.dup.gsub!(...)` at the mere cost of 2 unnecessary extra allocations due to String#dup

TBH I'm not sure we need yet another gsub method, but what gets me here is that `gsub?` is the primitive operation from which `gsub` and `gsub!` are made. Internally, these two methods work like this:

```ruby
def gsub!(...)
  modified = gsub?(...) and replace(modified)
end

def gsub(...)
  gsub?(...) or dup
end
```

We can efficiently derive these two methods from `gsub?`, but we cannot efficiently implement `gsub?` in ruby, so it feels regrettable to me that `gsub?` is not available as a built-in.

Use cases include:

```ruby
#ensure gsub has modified the string
newstr = str.gsub?(rx,repl) or raise "str did not contain expected value"

#take an action if the string is modified
if str = obj.title.gsub?(rx,repl)
  obj.title = str
  obj.save
end
```



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[ruby-core:120289] [Ruby master Feature#20885] String#gsub?

[matz (Yukihiro Matsumoto) via ruby-core]

Issue #20885 has been updated by matz (Yukihiro Matsumoto).


I am not positive for adding `gsub?`. It's not a predicate, after all.

Matz.


----------------------------------------
Feature #20885: String#gsub?
https://bugs.ruby-lang.org/issues/20885#change-111054

* Author: Dan0042 (Daniel DeLorme)
* Status: Open
----------------------------------------
I would like a variation of sub/gsub that returns a new string if there is a match, or nil otherwise.

This can be currently done with `str.dup.gsub!(...)` at the mere cost of 2 unnecessary extra allocations due to String#dup

TBH I'm not sure we need yet another gsub method, but what gets me here is that `gsub?` is the primitive operation from which `gsub` and `gsub!` are made. Internally, these two methods work like this:

```ruby
def gsub!(...)
  modified = gsub?(...) and replace(modified)
end

def gsub(...)
  gsub?(...) or dup
end
```

We can efficiently derive these two methods from `gsub?`, but we cannot efficiently implement `gsub?` in ruby, so it feels regrettable to me that `gsub?` is not available as a built-in.

Use cases include:

```ruby
# ensure gsub has modified the string
newstr = str.gsub?(rx,repl) or raise "str did not contain expected value"

# take an action if the string is modified
if str = obj.title.gsub?(rx,repl)
  obj.title = str
  obj.save
end

# avoid allocating a new string if there is no change
str = str.gsub?(rx,repl) || str
```



-- 
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 ______________________________________________
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[ruby-core:120301] [Ruby master Feature#20885] String#gsub?

[Dan0042 (Daniel DeLorme) via ruby-core]

Issue #20885 has been updated by Dan0042 (Daniel DeLorme).


Ah, you mean it doesn't return strictly true/false? That's a good point, although there are precedents like `Numeric#nonzero?`

But I'm not so attached to the name "gsub?" itself, it just happened to be the one that made the most sense to me. We could go with anything really. But I'm interested in discussing if this method, under another name, has a place in Ruby core.

----------------------------------------
Feature #20885: String#gsub?
https://bugs.ruby-lang.org/issues/20885#change-111067

* Author: Dan0042 (Daniel DeLorme)
* Status: Open
----------------------------------------
I would like a variation of sub/gsub that returns a new string if there is a match, or nil otherwise.

This can be currently done with `str.dup.gsub!(...)` at the mere cost of 2 unnecessary extra allocations due to String#dup

TBH I'm not sure we need yet another gsub method, but what gets me here is that `gsub?` is the primitive operation from which `gsub` and `gsub!` are made. Internally, these two methods work like this:

```ruby
def gsub!(...)
  modified = gsub?(...) and replace(modified)
end

def gsub(...)
  gsub?(...) or dup
end
```

We can efficiently derive these two methods from `gsub?`, but we cannot efficiently implement `gsub?` in ruby, so it feels regrettable to me that `gsub?` is not available as a built-in.

Use cases include:

```ruby
# ensure gsub has modified the string
newstr = str.gsub?(rx,repl) or raise "str did not contain expected value"

# take an action if the string is modified
if str = obj.title.gsub?(rx,repl)
  obj.title = str
  obj.save
end

# avoid allocating a new string if there is no change
str = str.gsub?(rx,repl) || str
```



-- 
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 ______________________________________________
 ruby-core mailing list -- ruby-core@ml.ruby-lang.org
 To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org
 ruby-core info -- https://ml.ruby-lang.org/mailman3/lists/ruby-core.ml.ruby-lang.org/