Oh, yes I see that now. Then what you could do is quote the call to names()
in your macro expression so the names call is executed in the calling
environment.
macro fetch(p)
return quote
local vars = names($p)
local ex = Expr(:block)
append!(ex.args, [:($v = $p.$v) for v in vars])
eval(ex)
end
end
This is similar to what yo have done at the REPL but it quotes the names()
call so it can get evaluated in the macro calling environment instead of
within the macro itself. ex = Expr(:block) is just another quote block
with a list of expressions to evaluate in ex.args. Note that there is no
need to use esc() here because the eval() call happens in the calling
environment.
On Monday, June 9, 2014 10:18:13 AM UTC-5, Andrew Simper wrote:
>
> Yes thanks for pointing that out, but if you look at this thread I already
> got some help with the |> esc for this type of thing over on another thread
> https://groups.google.com/forum/#!topic/julia-users/UvBff9QVKaA , but I
> started this thread specifically to find out how to get write a macro using
> names(obj) to do the work instead of having to write a new fetch macro
> manually every time I create a new type.
>
> On Monday, June 9, 2014 11:04:12 PM UTC+8, Nathaniel Nicandro wrote:
>>
>> You can use the esc
>> <http://julia.readthedocs.org/en/latest/stdlib/base/?highlight=esc#Base.esc>
>> function
>> that can introduce variables in the calling environment
>>
>> julia> type Point
>> x
>> y
>> end
>>
>> julia> macro fetch(p)
>> variables = quote
>> x = $p.x
>> y = $p.y
>> end
>> return esc(variables)
>> end
>>
>> julia> p = Point(5, 10)
>> Point(5,10)
>>
>> julia> x
>> ERROR: x not defined
>>
>> julia> y
>> ERROR: y not defined
>>
>> julia> @fetch p;
>>
>> julia> x
>> 5
>>
>> julia> y
>> 10
>>
>>
>>
>> On Saturday, June 7, 2014 2:35:59 AM UTC-5, Andrew Simper wrote:
>>>
>>> A lot of the time it is good to copy a structure to local variables and
>>> then process on those for efficiency before storing the local values back
>>> to a structure. To help out with this I'm trying to write a macro, so this
>>> is what I would like the end result to be:
>>>
>>> Point
>>> x::Float64
>>> y::Float64
>>> end
>>>
>>> function process (p::Point)
>>> local x = p.x;
>>> local y = p.y;
>>> # do some processing on x and y
>>> p.x = x
>>> p.y = y
>>> end
>>>
>>> and I would like write a macro that does this so the end code would like
>>> like:
>>>
>>> function process (p::Point)
>>> @fetch p
>>> # do some processing on x and y
>>> @store p
>>> end
>>>
>>> So far I've got this working at the REPL using:
>>>
>>> point = Point (1, 2)
>>> map (eval, ([:($name = point.$name) for name in names(point)]))
>>> println("x=$(x) y=$(y)")
>>>
>>> which prints out: x=1.0 y=2.0
>>>
>>> Can someone please help out turning this into a macro?
>>>
>>>
