Clojure defmacro丢失元数据 [英] Clojure defmacro loses metadata
问题描述
我想创建一个小的Clojure宏 def
sa类型提示的字符串:
(defmacro def-string [name value]
`(def ^ String〜name〜value))
(def-string db-host-option db-host)
当p macroexpand
它,类型提示丢失:
(宏展开式(def-string db-host-optiondb-host) )
; => (def db-host-optiondb-host)
不介意类型提示的智慧。
为什么宏丢失元数据?如何写这个宏或包含元数据的任何内容?
^
是读取器宏。 defmacro
永远不会看到它。提示放在列表(unquote name)
上。比较例子(meta ^ String'x)
与(meta'^ String x)
才能看到效果。 / p>
您需要在符号上加上提示。
(defmacro def-string
[name value]
`(def〜(vary-meta name assoc:tag`String)〜value))
而用法:
user => (def-string foobar)
#'user / foo
user => (meta#'foo)
{:ns#< Namespace user> ;,:name foo,:fileNO_SOURCE_PATH,:line 5,:tag java.lang.String}
I am trying to create a little Clojure macro that def
s a String with a type hint:
(defmacro def-string [name value]
`(def ^String ~name ~value))
(def-string db-host-option "db-host")
When I macroexpand
it, the type hint is lost:
(macroexpand '(def-string db-host-option "db-host"))
;=> (def db-host-option "db-host")
Never mind the wisdom of type hinting this.
Why is the macro losing the metadata? How do I write this macro, or any that includes metadata?
^
is a reader macro. defmacro
never gets to see it. The hint is put on the list (unquote name)
. Compare for example (meta ^String 'x)
with (meta ' ^String x)
to see the effect.
You need to put the hint on the symbol.
(defmacro def-string
[name value]
`(def ~(vary-meta name assoc :tag `String) ~value))
And the usage:
user=> (def-string foo "bar")
#'user/foo
user=> (meta #'foo)
{:ns #<Namespace user>, :name foo, :file "NO_SOURCE_PATH", :line 5, :tag java.lang.String}
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