4.11. Heredoc Terminators
Make every heredoc terminator a single uppercase identifier with a standard prefix .
You can use just about anything you like as a heredoc terminator. For example:
print <<'end list'; # Prints 3 lines then [DONE]
get name
set size
put next
end list
print "[DONE]\n";
or:
print <<''; # Prints 4 lines (up to the empty line) then [DONE]
get name
set size
put next
end list
print "[DONE]\n";
or even:
print <<'print "[DONE]\n";'; # Prints 5 lines but no [DONE]!
get name
set size
put next
end list
print "[DONE]\n";
Please don't. Heredocs are tough enough to understand as it is. Using bizarre terminators only makes them more difficult. It's a far better practice to stick with terminators that are capitalized (so they stand out better in mixed-case code) and free of whitespace (so only a single visual token has to be recognized).For example, compared to the previous examples, it's much easier to tell what the contents of the following heredoc are:
print <<'END_LIST';
get name
set size
put next
END_LIST
But even with a single identifier as terminator, both the contents and the termination marker of a heredoc still have to be left-justified. So it can still be difficult to detect the end of a heredoc. By naming every heredoc marker with a standard, easily recognized prefix, you can make them much easier to pick out.'END_...' is the recommended choice for this prefix. That is, instead of:
Readonly my $USAGE => <<"USAGE";
Usage: $0 <file> [-full] [-o] [-beans]
Options:
-full : produce a full dump
-o : dump in octal
-beans : source is Java
USAGE
delimit your heredocs like so:
Readonly my $USAGE => <<"END_USAGE";
Usage: $0 <file> [-full] [-o] [-beans]
Options:
-full : produce a full dump
-o : dump in octal
-beans : source is Java
END_USAGE
It helps to think of the << heredoc introducer as being pronounced "Everything up to...", so that the previous code reads as: the read-only $USAGE variable is initialized with everything up to END_USAGE.
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