[swift-users] Filling two type parameters with the same type

[Taylor Swift]

I have a type like

struct DistortedNoise<Source, Displacement> where Source:Noise,
Displacement:Noise
{
    let source:Source,
        displacement:Displacement

    init(source:Source, displacement:Displacement)
    {
        self.source       = source
        self.displacement = displacement
    }

    init(source:Source)
    {
        self.source       = source
        self.displacement = source
    }
}

and I get the error

Compile Swift Module 'Noise' (5 sources)
/home/taylor/noise/sources/noise/noise.swift:576:29: error: 'Source' is not
convertible to 'Displacement'
        self.displacement = source
                            ^~~~~~

How do I tell Swift that I want the same type fulfilling both Source and
Displacement?
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