# The difference between := and =<

### 12.2.10 The difference between := and =<

The := and =< assignment operators have different effects when they are used to modify an element of a list contained in a variable, since =< modifies the element by reference. Otherwise, they will have the same effect.

#### Example.

Input:

A:= [1,2,3]

Here:

A[1]:= 5

and

A[1] =< 5

both change A[1] to 5:
Input:

A

Output:

⎡ ⎣ | 1,5,3 | ⎤ ⎦

but they do it in different ways. The command A[1] =< 5 changes the middle value in the list that A originally pointed to, and so any other variable pointing to the list will be changed, but A[1]:= 5 will create a duplicate list with the middle element of 5, and so any other variable pointing to the original list won’t be affected.

#### Examples.

- Input:

  A:=[0,1,2,3,4]
  B:=A
  B[3]=<33
  A,B

  Output:

  ⎡ ⎣ | 0,1,2,33,4 | ⎤ ⎦ | , | ⎡ ⎣ | 0,1,2,33,4 | ⎤ ⎦

- Input:

  A:=[0,1,2,3,4] B:=A B[3]:=33 A,B

  Output:

  ⎡ ⎣ | 0,1,2,3,4 | ⎤ ⎦ | , | ⎡ ⎣ | 0,1,2,33,4 | ⎤ ⎦

If B is set equal to a copy of A instead of A, then changing B won’t affect A.

#### Example.

Input:

A:=[0,1,2,3,4] B:=copy(A) B[3]=<33 A,B

Output:

⎡ ⎣ | 0,1,2,3,4 | ⎤ ⎦ | , | ⎡ ⎣ | 0,1,2,33,4 | ⎤ ⎦