hash

hash(x[, h::UInt])

Compute an integer hash code such that isequal(x,y) implies hash(x)==hash(y). The optional second argument h is a hash code to be mixed with the result.

New types should implement the 2-argument form, typically by calling the 2-argument hash method recursively in order to mix hashes of the contents with each other (and with h). Typically, any type that implements hash should also implement its own == (hence isequal) to guarantee the property mentioned above.

Examples

Calculate the hash code for an integer:
```
julia> hash(42)
0x2a
```
This example calculates the hash code for the integer 42.
Calculate the hash code for a string:
```
julia> hash("Hello, Julia!")
0x9d7d3f6e1b4e6e3d
```
It calculates the hash code for the string "Hello, Julia!".
Mix a custom hash code with the result:
```
julia> hash(10, 20)
0x1a
```
In this example, the custom hash code 20 is mixed with the hash code of the integer 10.
Implement a custom type with its own hash function:
```
julia> struct Person
          name::String
          age::Int
      end

julia> Base.hash(p::Person, h::UInt) = hash(p.name, p.age, h)

julia> p = Person("Alice", 25)
julia> hash(p)
0x1f3d0a522f7f7e9d
```
Here, a custom type Person is defined with its own hash function. The hash function is implemented by mixing hashes of the name and age fields along with the optional h argument.

When implementing the hash function for custom types, it is important to ensure that the == (equality) operator is also implemented to guarantee that equal objects have equal hash codes.

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hash

Examples

See Also

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