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Re^5: Effeciency of key-only hash

by betterworld (Curate)
on Aug 24, 2008 at 22:34 UTC ( #706594=note: print w/replies, xml ) Need Help??


in reply to Re^4: Effeciency of key-only hash
in thread Effecicncy of key-only hash

you can shave off two characters by omitting the parentheses.

If you want to omit characters, you can write

my %hash = map $_=>1, qw(shave the modern way);

Update: I'm sorry, I should have tested this code... thanks to lodin, see below.

(Not to mention the whitespace... but often some more characters make the code more readable.)

I find it quite natural that map uses list context and grep uses scalar context. grep's block evaluates to a boolean value (whether or not to include the element), which is a scalar. map's block evaluates to... well, a list. If this were not the case, the parentheses would not help.

One remark about this "map" solution: Note that this works only once. If you use the hash-slice solution, you can add something to the set several times.

Replies are listed 'Best First'.
Re^6: Effeciency of key-only hash (map EXPR => LIST)
by lodin (Hermit) on Aug 25, 2008 at 20:08 UTC

    If you want to omit characters, you can write
    my %hash = map $_=>1, qw(shave the modern way);

    Interestingly, you can't. If you want to remove the block you need to have

    map +($_ => 1), ...
    as => is a comma, so what you actually wrote is equivalent to these two statements below.
    my %hash = map $_, 1, qw(shave the modern way); my %hash = map { $_ } 1, qw(shave the modern way);

    (If you write map ($_ => 1), LIST the "function rule" kicks in and it becomes map($_ => 1), LIST i.e. (map $_, 1), LIST.)

    This means that you can write

    map f($_) => LIST
    which one could read declaratively as "map the function f onto the list I'm pointing at". Personally though I usually think of map as acting in the other direction, "shifting" of one element at a time from the list.

    lodin

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