I have a number of variables based on composite types. I want the fields of
these variables synced to disk, so that every time I modify a field, the
data is written to disk. Is there any way to do this with assignment
notation?
For example,
type Foo
x::Int32
y::Int16
z::Int16
function Foo(x,y,z)
s = stream("foo",true, true, true, false, false)
write(s, x)
write(s, y)
write(s, z)
end
end
f=Foo(1,2,3)
...
f.z = 4
The constructor will write the initial values to disk. What kind of code
can I add to this program so that the assignment of f.z seeks to the disk
location where z is stored and writes the new value. I don't mind
implementing a function like
function update(value, name::Symbol, x)
T = type(value)
index = indexin([:x], convert(Array{Symbol,1},names(T)))
seek(s, fieldoffsets(T)[index])
write(s, x)
setfield(value, name, x)
end
but I don't want to have to call update(f, :z, 4) everywhere in the code
that wants to change f. I want to write f.z=4. Otherwise, the user of my
type may forget and cause inconsistency between data in memory and data on
disk.
I know that some languages have triggers, where a function can be called
when a variable is modified, and I know that I can write functions to
replace operators in Julia. But I cannot find any such trigger
functionality in Julia, nor can I seem to override the assignment operator
(=).
function =(x, v)
...
end
doesn't work; it tells me "syntax: unexpected =".
The docs state that there is a setfield! function that is called for a.b =
c, but the language disagrees. Apparently it's actually named setfield (no
exclamation point). And it's not a function I can replace.
setfield(x, name::Symbol, value) = println("$name")
reports "invalid method definition: not a generic function". So, setfield
cannot be overridden.
Do I have any options?
Thanks,
Keith
