# make -f assignment_variants.make A=1 B=2 C=3 D=4
# 1
# 2
# 3
# 4

# A=1 B=2 C=3 D=4 make -f assignment_variants.make
# A
# B
# 3
# 4 D

A  = A
B := B
C ?= C
D += D

all:
	@echo $(A)
	@echo $(B)
	@echo $(C)
	@echo $(D)