[swift-evolution] multi-line string literals

[Travis Tilley]

I would very much like to implement multi-line string literals in swift and
get feedback on what this should look like, as i've been informed there are
several competing suggestions filed as radars.

My initial improvement request is here: https://bugs.swift.org/browse/SR-170

It is only an opinion, but it's my belief that simple python-style
multi-line string literals are the way to go. They're simple and, in the
end, exactly the same as normal string literals. They begin and end with
triple quotes, can contain newlines, can contain single quotes, and that's
all that's special in their parsing. The same block of code in Lexer.cpp
could be used for both types of literal, ensuring behavior is always
consistent regardless of any future changes.

There is also the potential suggestion of removing consistent indentation
if there is any so as to make formatting of a multi-line string literal
look more clean when indented. For me, it would be a nice to have, but not
a make or break feature... and for some it may be confusing.

I'd like to state that I'm not proposing heredoc-style functionality, as I
believe that to be an entirely separate feature. The potential to have one
heredoc embedded within another would certainly make parsing more painful
than i'm happy with.

For an example of code that would benefit significantly from multi-line
string literals, please look at docopt.swift:
https://github.com/docopt/docopt.swift/blob/master/Examples/Swift/arguments_example/main.swift#L9-L25

Docopt does the opposite of what most command line argument libraries do:
rather than defining options and auto-generating the help text based on
that... You write the help text and it auto-generates a CLI with exactly
those options and arguments. It makes writing CLI applications an absolute
pleasure, but without multi-line string literals in swift it's currently
less pleasant than it could be.

Please send me your thoughts. ^_^b


-Travis Tilley
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