| Map method bug? [message #90061] |
Wed, 21 January 2015 15:48  |
penteado
Messages: 866
Registered: February 2018
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Senior Member
Administrator |
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Hello,
I had been trying to debug some crazy results I got in a program, and I tracked it down to what appears to be a bug in the map method. It seems that if I pass to map a lambda function that takes a structure as a second argument, it either returns a wrong value, o IDL segfaults. Here is one example:
IDL> compile_opt idl2
IDL> s=replicate({a:0B},3) & s.a=bindgen(3)
IDL> lam1=lambda(x,y:typename(y))
IDL> l=[1,0,1]
IDL> foreach ll,l,il do print,il,ll,' ',lam1(ll,s)
0 1 STRUCT
1 0 STRUCT
2 1 STRUCT
So far, so good. This was just to show that this simple lambda function works as expected, taking elements from l as input. But then:
IDL> l.map(lam1,s)
Segmentation fault (core dumped)
On some other cases, it did not segfault, it only gave me a wrong answer. Continuing with the structure s defined above:
IDL> l2=list([1,1,0],[0,1])
IDL> l2.map(lambda(x,y:x*y),-1)
[
[-1, -1, 0],
[0, -1]
]
IDL> lam2=lambda(x,y:(y[x]).a)
IDL> foreach ll,l2,il do print,lam2(ll,s)
1 1 0
0 1
All Ok so far. However, mapping lam2 into l2 gives nonsense:
IDL> l2.map(lam2,s)
[
[0, 0, 0],
[1, 1]
]
So far, I have only noticed this problem with 2-argument lambda functions, with the second argument being a structure. The second example looks like a bug to me - the first one must be a bug, since nothing done with just IDL code should ever cause a segfault.
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