将表达式内插到表达式中 [英] Interpolating an Expression into an Expression
问题描述
我想用宏内部的关键字参数构建一个构造函数,并且第一个关键字参数需要用于表达式.我在将该表达式放入表达式时遇到麻烦.这就是我的意思.说我有类型
I want to build a constructor with keyword arguments inside of a macro, and the first keyword argument needs to be for an expression. I am having trouble putting that expression into the expression. Here's what I mean. Say I have a type
type Test
ex
end
其中包含一个表达式.我想创建一个构造函数,其中origex = :(a * b)
是关键字参数的默认构造函数.我尝试过
which holds an expression. I want to make a constructor where origex = :(a * b)
is the default from a keyword argument. I tried
@eval :(Test(ex=$origex) = Test(origex))
但是,如果您看一下这样的表达式:
But if you look at the expression that makes:
Test(ex=a * b) = begin # console, line 1:
Test(origex)
end
您会看到它不起作用,因为a*b
仍需要是一个表达式.所以我尝试了
you see that it won't work because the a*b
needs to still be an expression. So I tried
@eval :(Test(ex=:($origex)) = Test(origex))
但是这个表达式很奇怪
Test(ex=$(Expr(:quote, :($(Expr(:$, :origex)))))) = begin # console, line 1:
Test(origex)
end
,也不会eval
.相反,我需要获取
which also won't eval
. Instead I need to get
Test(ex=:(a * b)) = begin # console, line 1:
Test(origex)
end
作为eval的表达式,但我不知道如何将该表达式转换为表达式.
as the expression to eval, but I don't know how to get that expression into an expression.
推荐答案
我认为以下是您想要的.您似乎犯了一些错误:
I think the following is what you want. You seem to have had a few mistakes:
julia> type Test
ex::Expr
end
julia> orig_ex = :(a + b)
:(a + b)
julia> new_ex = Meta.quot(orig_ex)
:($(Expr(:quote, :(a + b))))
julia> code = :( Test(; ex=$new_ex) = Test(ex) )
:(Test(; ex=$(Expr(:quote, :(a + b)))) = begin # REPL[4], line 1:
Test(ex)
end)
julia> eval(code)
Test
julia> Test()
Test(:(a + b))
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