Course of Raku / Advanced / Containers / Contexts 🆕

Numeric, string, and Boolean context

Three very common contexts ask a value to behave as a number, a string, or a Boolean value. Each has a prefix operator that forces it explicitly:

• + — numeric context
• ~ — string context
• ? — Boolean context

Applied to an array, they give its length, its elements joined by spaces, and whether it has any elements:

my @a = 1, 2, 3;

say +@a; # 3
say ~@a; # 1 2 3
say ?@a; # True

An empty array is 0 in numeric context and False in Boolean context:

my @empty;
say +@empty; # 0
say ?@empty; # False

You don’t need to always write these operators by hand, because the language can impose the right context for you. Arithmetic puts its operands in numeric context, concatenation puts them in string context, and if, while, and and/or put their condition in Boolean context:

my @a = 1, 2, 3;

say 10 + @a;              # 13, here @a is its length: 3
say 'items: ' ~ @a;       # items: 1 2 3
if @a { say 'not empty' } # not empty

So if @array { … } works exactly as you would hope: a non-empty array is true. The prefix operators are the explicit way to ask for the same coercions.

In a compination with a postfix if, this allows to create really expressive code:

say "{+@a} items are there" if @a; # 3 items are there

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