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I'm reviewing a line of Ruby code in a pull request. I'm not sure if this is a bug or a feature that I haven't seen before:
puts "A string of Ruby that"\
"continues on the next line"
Is the backslash a valid character to concatenate these strings? Or is this a bug?
313
The backslash is a line continuation. Your code has two quoted runs of text; the runs appear like two strings, but are really just one string because Ruby concatenates whitespace-separated runs. Caution: + continues the statement but not the string. puts "foo"+"bar".
In double quoted strings, you can write escape sequences and Ruby will output their translated meaning. A \n becomes a newline. In single quoted strings however, escape sequences are escaped and return their literal definition. A \n remains a \n .
The easiest way to create a multiline string is to just use multiple lines between quotation marks: address = "Four score and seven years ago our fathers brought forth on this continent, a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal."
"\n" is newline, '\n\ is literally backslash and n.
That is valid code.
The backslash is a line continuation. Your code has two quoted runs of text; the runs appear like two strings, but are really just one string because Ruby concatenates whitespace-separated runs.
Example of three quoted runs of text that are really just one string:
"a" "b" "c" => "abc" Example of three quoted runs of text that are really just one string, using \ line continuations:
"a" \ "b" \ "c" => "abc" Example of three strings, using + line continuations and also concatenations:
"a" + "b" + "c" => "abc" Other line continuation details: "Ruby interprets semicolons and newline characters as the ending of a statement. However, if Ruby encounters operators, such as +, -, or backslash at the end of a line, they indicate the continuation of a statement." - Ruby Quick Guide
190
The backslash character does not concatenate any strings. It prevents the line-break from meaning that those two lines are different statements. Think of the backslash as the opposite of the semicolon. The semicolon lets two statements occupy one line; the backslash lets one statement occupy two lines.
What you are not realizing is that a string literal can be written as multiple successive literals. This is legal Ruby:
s = "A string of Ruby that" "continues on the same line" puts s Since that is legal, it is legal to put a line break between the two string literals - but then you need the backslash, the line-continuation character, to tell Ruby that these are in fact the same statement, spread over two lines.
s = "A string of Ruby that" \ "continues on the same line" puts s If you omit the backslash, it is still legal, but doesn't give the result you might be hoping for; the string literal on the second line is simply thrown away.
25
This is not a case of concatenated strings. It is one single string. "foo" "bar" is a syntactic construct that allows you to break up a string in your code, but it is identical to "foobar". In contrast, "foo" + "bar" is the true concatenation, invoking the concatenation method + on object "foo".
You can verify this by dumping the YARV instructions. Compare:
RubyVM::InstructionSequence.compile('"foo" + "bar"').to_a
// .... [:putstring, "foo"], [:putstring, "bar"] ....
RubyVM::InstructionSequence.compile('"foo" "bar"').to_a
// .... [:putstring, "foobar"] ....
The backslash in front of the newline will cancel the newline, so it does not terminate the statement; without it, it would not be one string, but two strings in separate lines.
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