Julia 1.0 Programming Complete Reference Guide

Learning about pairs

While looking at the response header, you might've noticed that its type is an Array of Pair objects:

julia> resp.headers 
25-element Array{Pair{SubString{String},SubString{String}},1} 

A Pair represents a Julia data structure—and the corresponding type. The Pair contains a couple of values that are generally used to reference key-value relationships. The types of the two elements determine the concrete type of the Pair.

For example, we can construct a Pair with the following:

julia> Pair(:foo, "bar") 
:foo => "bar" 

If we check its type we'll see that it's a Pair of Symbol and String:

julia> typeof(Pair(:foo, "bar")) 
Pair{Symbol,String} 

We can also create Pairs by using the x => y literal notation:

julia> 3 => 'C' 3 => ...