Default return value for find functions when no match found


#1

For v0.7 the find functions return nothing when no match is found.

Would it be convenient to provide a default parameter to return if no match is found, similar to the get function?

For example:

findlast(!iszero, A, 0)

would return 0 if there is no match.

(then effectively findlast(pred, A) = findlast(pred, A, nothing)


#2

Seems like you could define a similar one line function that does what you want. If the base function returns nothing, you set it to the extra parameter.


#3

The issue with that would be efficiency.
For strings, for example, where any valid index is guaranteed to be > 0, using 0 for the sentinel can be more efficient than returning nothing, and then to have to test for nothing just to turn it back into a 0, seems sad.
(esp. since some of the internal code in base actually returns 0, and then checks for that,
and returns nothing instead!)


#4

Well of course I can define my own methods, but my question was would this be more widely useful.

Is so, there could be a standard implementation in Base, which would obviate separate custom implementations and promote idiomatic use.

In any case, here’s what I’ve defined for my purpose:

v0.6

Base.findlast(pred::Function, A, default) = 
    (i = findlast(pred, A); i in linearindices(A) ? i : default)

v0.7

Base.findlast(pred::Function, A, default) =
    (i = findlast(pred, A); i == nothing ? default : i)

And similarly for other find functions.