Summary

In R, the return statement is not strictly required in functions.

# this returns NULL
gives_nothing <- function(x, y){
    print(x)
    print(y)
}

# this returns the value of n
gives_sum <- function(x, y){
    n <- x + y
    n
}

This means that it can sometimes be difficult to understand, from looking at the code, what a function will return.

How

Problem:
catboost version: 0.23.2
Operating System: all
Tutorial: https://github.com/catboost/tutorials/blob/master/custom_loss/custom_metric_tutorial.md

Impossible to use custom metric (С++).

Code example

from catboost import CatBoost
train_data = [[1, 4, 5, 6],