bash - The function definitions in shell use dash

The following code：

#!/bin/bash


function me-test()
{
        echo 'test'
}

me-test

The execution method below is not correct：

#sh 1.sh
1.sh: line 6: `me-test': not a valid identifier

but the execution method below is correct:

#./1.sh
test

In other programming languages,it can not using dash to define function.For example,python.

why shell is so that?