[ruby-core:71386] [Ruby trunk - Feature #11661] [Feedback] sprintf causes a KeyError instead of using a default value for hash substitution

[nobu@ruby-lang.org]

Issue #11661 has been updated by Nobuyoshi Nakada.

Tracker changed from Bug to Feature
Status changed from Open to Feedback

[GH-1087](https://github.com/ruby/ruby/pull/1087) doesn't work properly with a default proc expecting an argument, but segfaults.

My patch.

~~~diff
diff --git i/sprintf.c w/sprintf.c
index 705d3ce..eee5695 100644
--- i/sprintf.c
+++ w/sprintf.c
@@ -605,13 +605,10 @@ rb_str_format(int argc, const VALUE *argv, VALUE fmt)
 		}
 		CHECKNAMEARG(start, len, enc);
 		get_hash(&hash, argc, argv);
-		sym = rb_check_symbol_cstr(start + 1,
-					   len - 2 /* without parenthesis */,
-					   enc);
-		if (sym != Qnil) nextvalue = rb_hash_lookup2(hash, sym, Qundef);
-		if (nextvalue == Qundef) {
-		    rb_enc_raise(enc, rb_eKeyError, "key%.*s not found", len, start);
-		}
+		sym = rb_cstr_intern(start + 1,
+				     len - 2 /* without parenthesis */,
+				     enc);
+		nextvalue = rb_hash_aref(hash, sym);
 		if (term == '}') goto format_s;
 		p++;
 		goto retry;
~~~

----------------------------------------
Feature #11661: sprintf causes a KeyError instead of using a default value for hash substitution
https://bugs.ruby-lang.org/issues/11661#change-54757

* Author: Eddy Luten
* Status: Feedback
* Priority: Normal
* Assignee: Yukihiro Matsumoto
----------------------------------------
When using a format string that substitutes hash values (or using the `%` operator on a string), instead of using the Hash's default value if a key is not present, it causes a KeyError.

As an end-user, to get around this, my hash needs to know about all the possible keys ahead of time and pre-assign a value to them or handle the KeyError. Logically, I would assume that the `sprintf` implementation would use the default Hash value.

I wanted to open this issue to see what your collective thoughts were on this since I have a fork running locally that fixes this issue and was wondering if I could send a patch/PR for this.

This issue is reproducible using the following code:

```ruby
my_hash = Hash.new('world')
puts "hello %{location}" % my_hash # expecting "hello world"
# "KeyError: key{location} not found"
```



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