Multiton: Difference between revisions
julia example
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* [[Singleton]]
<br><br>
=={{header|Julia}}==
A registry (just in memory, not on disk) is used below instead of an enum. The registry is protected by a lock on the Multiton constructor, to prevent two threads creating the same object at the same time.
<lang julia>struct Multiton{T}
data::T
function Multiton(registry, refnum, data)
if 0 < refnum <= registry.max_instances && registry.instances[refnum] isa Nothing
lock(registry.spinlock)
multiton = new{typeof(data)}(data)
registry.instances[refnum] = multiton
unlock(registry.spinlock)
return multiton
else
error("Cannot create instance with instance reference number $refnum")
end
end
function Multiton(registry, refnum)
if 0 < refnum <= registry.max_instances && registry.instances[refnum] isa Multiton
return registry.instances[refnum]
else
error("Cannot find a Multiton in registry with instance reference number $refnum")
end
end
end
struct Registry
spinlock::Threads.SpinLock
max_instances::Int
instances::Vector{Union{Nothing, Multiton}}
Registry(maxnum) = new(Threads.SpinLock(), maxnum, fill(nothing, maxnum))
end
reg = Registry(3)
m0 = Multiton(reg, 1, "zero")
m1 = Multiton(reg, 2, 1.0)
m2 = Multiton(reg, 3, [2])
m3 = Multiton(reg, 1)
m4 = Multiton(reg, 2)
for m in [m0, m1, m2, m3, m4]
println("Multiton is $m")
end
# produce error
# m3 = Multiton(reg, 4, "three")
# produce error
m5 = Multiton(reg, 5)
</lang>{{out}}
<pre>
Multiton is Multiton{String}("zero")
Multiton is Multiton{Float64}(1.0)
Multiton is Multiton{Vector{Int64}}([2])
Multiton is Multiton{String}("zero")
Multiton is Multiton{Float64}(1.0)
ERROR: LoadError: Cannot find a Multiton in registry with instance reference number 5
</pre>
=={{header|Wren}}==
{{libheader|Wren-dynamic}}
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