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isa

isa(x, type) -> Bool

Determine whether x is of the given type.

Examples

1. Check if a value is of a specific type:

   julia> x = 10;
   julia> isa(x, Int)
   true

   This example checks if the value x is of type Int.

2. Verify type compatibility with abstract types:

   julia> y = [1, 2, 3];
   julia> isa(y, AbstractArray)
   true

   It confirms that y is of type AbstractArray, which includes all array-like types in Julia.

3. Check for subtype relationship with user-defined types:

   julia> struct Person end;
   julia> struct Student <: Person end;
   julia> s = Student();
   julia> isa(s, Person)
   true

   In this example, isa verifies that s is of type Person, even though it is an instance of the subtype Student.

Common mistake example:

julia> a = 5;
julia> isa(a, Float64)
false

In this case, the mistake is expecting isa to return true for a being of type Float64. However, since a is an integer (Int), it is not of the requested type. It's essential to understand the type hierarchy and use isa appropriately to avoid such errors.

See Also

User Contributed Notes

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