El lunes, 30 de mayo de 2016, 19:11:47 (UTC-4), FANG Colin escribió: > > function t1(n::Int, x::Int, a::Float64) > x::Float64 = x > for i in 1:n > x += a > end > x > end > @time t1(10^6, 1, 1.0) > > 0.005445 seconds (1.00 M allocations: 15.259 MB) >
In t1, x changes type during the function, from Int to Float64, so the function is type *un*stable, as shown by @code_warntype, and as suggested by the huge number of allocations. In t2, x is always a Float64, and the function is type stable. > > > > > function t2(n::Int, y::Int, a::Float64) > x::Float64 = y > for i in 1:n > x += a > end > x > end > @time t2(10^6, 1, 1.0) > > 0.001044 seconds (6 allocations: 192 bytes) > > > > > The @code_warntype of the 2 functions are very similar. However, the llvm > code generated from t2 is a lot simpler. > The @code_warntype of the two functions is very *different*. (This is easier to see in the REPL than in the notebook, if that is the problem.) > > Does it suggest that if we want to change the type of an argument, we'd > better create a new variable? >
