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Yuichiro Kaneko
Crystal
×
macro
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ࣗݾհ
• @yui-knk (github) / @spikeolaf (twitter)
• docrails commiter
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RailsΨΠυ༁νʔϜ
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Crystal ͷੈքͰ
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No content
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0.7.5 release!!
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ϚΫϩ??
• Macros are methods that receive AST nodes
at compile-time and produce code that is
pasted into a program.
• ίϯύΠϧ࣌ʹɺASTϊʔυΛ͏͚ͱͬͯɺ
ίʔυΛฦ͢Α͏ͳϝιουɻ
• http://crystal-lang.org/docs/syntax_and_semantics/macros.html
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Example.1
# ϚΫϩΛఆٛ͢Δ
macro define_method(name, content)
def {{name.id}}
{{content}}
end
end
!
# ϚΫϩΛల։͢Δ
define_method :foo, 1
# def foo
# 1
# end
!
# ϝιουΛݺͼग़͢
foo
# => 1
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Example.2 (for)
# ϚΫϩΛఆٛ͢Δ
macro define_dummy_methods(names)
{% for name, index in names %}
def {{name.id}}
{{index}}
end
{% end %}
end
!
# ϚΫϩΛల։͢Δ
define_dummy_methods [foo, bar, baz]
# def foo
# 0
# end
# …
!
foo # => 0
bar # => 1
baz # => 2
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Example.3 (yield)
# ϚΫϩΛఆٛ͢Δ
macro test_with
p "before"
{{yield}}
p "after"
end
!
# ϚΫϩΛల։͢Δ
test_with do
p "in block"
end
# p "before"
# p "in block"
# p "after"
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ϚΫϩ??
• Macros are methods that receive AST nodes
at compile-time and produce code that is
pasted into a program.
• ίϯύΠϧ࣌ʹɺASTϊʔυΛ͏͚ͱͬͯɺ
ίʔυΛฦ͢Α͏ͳϝιουɻ
• http://crystal-lang.org/docs/syntax_and_semantics/macros.html
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Example.4
# ϚΫϩΛఆٛ͢Δ
macro test_print
{{p "before"}}
{{yield}}
{{p "after"}}
end
!
# ϚΫϩΛల։͢Δ
test_print do
p "in block"
end
# “before" (printed)
# “after" (printed)
#
# p "in block"
#
ϚΫϩల։࣌ʹQSJOUͯ͠OJMΛฦ͢
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ϚΫϩ??
• Macros are methods that receive AST nodes
at compile-time and produce code that is
pasted into a program.
• ίϯύΠϧ࣌ʹɺASTϊʔυΛ͏͚ͱͬͯɺ
ίʔυΛฦ͢Α͏ͳϝιουɻ
• http://crystal-lang.org/docs/syntax_and_semantics/macros.html
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Example.5 (StringLiteral)
# ͜Εok
{{"hoge".upcase}}
# "HOGE"
!
# ͜Εok
"1".to_i
# =>1
!
# ͜Εng
{{"1".to_i}}
!
Error in test.cr:1: expanding macro
!
{{"1".to_i}}
^
!
in test.cr:1: undefined macro method 'StringLiteral#to_i'
!
{{"1".to_i}}
^~~~
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Example.6 (#class_name)
from 0.7.5
macro print_class_names(*nodes)
{% for node in nodes %}
{{p node.class_name}}
{% end %}
end
!
print_class_names(“1")
# “StringLiteral"
print_class_names([1])
# “ArrayLiteral"
print_class_names({a: 10})
# “HashLiteral"
print_class_names(foo)
# “Call"
print_class_names(true ? 1 : 0)
# “If"
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Example.6 (#class_name)
from 0.7.5
print_class_names(
if true
1
else
0
end
)
# “If"
print_class_names(
class
Foo
end
)
# “ClassDef"
print_class_names(
def test_method
end
)
# “Def"
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Example.6 (#class_name)
from 0.7.5
print_class_names(
if true
1
else
0
end,
class MyClass
end
)
# “If"
# “ClassDef"
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http://crystal-lang.org/api/
index.html
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Example.7 (my_unless)
macro my_unless(cond, then_exp, else_exp = nil)
if {{ cond }}
{{ else_exp }}
else
{{ then_exp }}
end
end
!
def ten?(a)
a == 10
end
!
my_unless(
ten?(11),
p("false case"),
p("true case")
)
# "false case"
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Example.8 (visibility)
class MyClass
def public_method
end
!
protected def protected_method
end
!
private def private_method
end
!
{% for m in @type.methods %}
{{p m.name}}
{{p m.visibility}}
{% end %}
end
# public_method
# :public
# protected_method
# :protected
# private_method
# :private
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·ͱΊ
• ruby like syntaxͰcompilerͱ͔ಡΊΔ
• macro def ͱ͔ @type ͷ͜ͱௐ͍ͨ
• ASTNodeͷprinter΄͍͠
• ύʔαδΣωϨʔλʔɾɾɾ