Feature #3450: Format Strings with Named Arguments & Hash#default

• Status: Closed
• Assignee: nobu (Nobuyoshi Nakada)
• Target version: 2.6

[runpaint (Run Paint Run Run)]

=begin
Is it intentional that the, undocumented, feature #442 (named arguments in format strings) ignores the Hash's default value?

hash = {greeting: 'Hello'}.tap{|h| h.default = 'World'}
'%{greeting}, %{greeted}' % hash
#=> KeyError: key{greeted} not found

It's quite common for templates to use default values. In interface localisation, untranslated strings may need to be substituted for the equivalent in the native language, or replaced with a generic string in the target language. When building reports with format strings, a default value of an empty string allows unexpanded format sequences to be non-fatal. In both cases, a default proc would provide even further flexibility.

Another perspective is that this behavior unnecessarily breaks the abstraction that default values are just like any other.
=end

[judofyr (Magnus Holm)]

• File 3450.patch 3450.patch added

=begin
I believe this patch should fix it, but this also has the side effect that KeyError will never be raised (since it will always use the default value, which is nil be default). There's probably some more code which can be removed if we apply the patch, but it seems to me that this is intentional behaviour though…
=end

[nahi (Hiroshi Nakamura)]

• Description updated (diff)
• Assignee set to nobu (Nobuyoshi Nakada)

[shyouhei (Shyouhei Urabe)]

• Status changed from Open to Assigned

[mame (Yusuke Endoh)]

• Target version changed from 2.0.0 to 2.6

[nobu (Nobuyoshi Nakada)]

I think this is a trade-off.
Silently ignoring undefined keys may not preferable for somebody.
I don't think differentiating simple default value and default proc is good idea.

[matz (Yukihiro Matsumoto)]

• Status changed from Assigned to Closed

Already fixed.

Matz.