This definition in isolation doesn’t really “mean” anything; it is just a user defined
struct with one field (called
layers) and one inner constructor. Usually custom structs like this is used for collecting some data and/or used to define operations on, e.g. you could define a function
f operating on this struct like this:
function f(c::Chain) # do something with the layers in the chain end
but in order to understand what it is used for in this specific case you probably need to consult the documentation and/or the rest of the code.
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