Check if Contract variable is undefined

Question

How can I check if an Contract variable is undefined in Solidity?

score 8 · Answer 1 · edited Jun 16 '20 at 10:58

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According to this

Memory-stored objects as local variables are correctly zero-initialised: Members of structs and elements of fixed-size arrays are recursively initialised, dynamic arrays are set to zero length. delete x assigns a new zero-initialised value to x.

There is no such undefined variable. All objects are zero-initalised.

edited Jun 16 '20 at 10:58

Community

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answered Mar 31 '16 at 12:37

Loi.Luu

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score 4 · Answer 2 · answered Mar 31 '16 at 14:25

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By some Solidity coding conventions you add a boolean 'valid' element to any struct to indicate it is undefined (false is the initialized value).

Sometimes I see fields having zero reserved to mean undefined - e.g. treat 0 as an undefined address. You could also do that for a string, but string is often externally input so you have to make sure someone didn't send you a zero string.

I would advise using a field where zero is naturally meaningful like a separate bool or an existing address element in a struct.

answered Mar 31 '16 at 14:25

Paul S

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This is not useful for a pure Contract object isn't it? – arodriguezdonaire Mar 31 '16 at 14:31
what do you mean by a "pure Contract object"? – Paul S Mar 31 '16 at 19:44

Check if Contract variable is undefined

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