join: assert that by() vars have same general type (str vs num) about ftools HOT 1 OPEN

* generate data
clear

* master dataset
set seed 09092019
set obs 10
gen string_id = "A"
replace string_id = "B" if _n > 5
gen number_id = int(runiform() * 2)
save temp_master_dataset, replace

* using dataset
duplicates drop
gen usingvar = "BLA" * (number_id + 1)
tostring number_id, gen(number_id_tostring)
save temp_using_dataset, replace

use master, clear
* error when joining
join, from(temp_using_dataset) by(string_id number_id)

* case with no error when using only strings
tostring number_id, gen(number_id_tostring)
join usingvar, from(temp_using_dataset) by(string_id number_id_tostring)