[julia-users] Define `similar` function for a custom array

[Wai Yip Tung]

I have successfully defined a custom array Ngram.

type Ngram <: AbstractArray{ASCIIString,1}
    seq::ASCIIString
    n::Int
end

function getindex(s::Ngram, i::Int)
    s.seq[i:i+s.n-1]
end

function Base.size(s::Ngram)
    length(s.seq) - s.n + 1
end


It works as I expected. For example

In [219]:

ng=SeqUtil.Ngram("hello",2)

Out[219]:

4-element Ngram:
 "he"
 "el"
 "ll"
 "lo"


But it seems in other usage, a corresponding `similar` method is necessary

In [222]:

map(print,ng)

he

`similar` has no method matching similar(::Ngram, ::Type{Nothing}, ::(Int32,))
while loading In[222], in expression starting on line 1

 in similar at abstractarray.jl:116
 in map at abstractarray.jl:1329


I have read the documentation and I still don't get what I need to do in 
the similar method. You help will be appreciated.

Wai Yip