| 1 | # SPDX-License-Identifier: GPL-2.0 |
| 2 | |
| 3 | # Shorthand |
| 4 | warning = $(warning-if,y,$(1)) |
| 5 | |
| 6 | # Simply expanded variable. |
| 7 | X := 1 |
| 8 | SIMPLE := $(X) |
| 9 | X := 2 |
| 10 | $(warning,SIMPLE = $(SIMPLE)) |
| 11 | |
| 12 | # Recursively expanded variable. |
| 13 | X := 1 |
| 14 | RECURSIVE = $(X) |
| 15 | X := 2 |
| 16 | $(warning,RECURSIVE = $(RECURSIVE)) |
| 17 | |
| 18 | # Append something to a simply expanded variable. |
| 19 | Y := 3 |
| 20 | SIMPLE += $(Y) |
| 21 | Y := 4 |
| 22 | $(warning,SIMPLE = $(SIMPLE)) |
| 23 | |
| 24 | # Append something to a recursively expanded variable. |
| 25 | Y := 3 |
| 26 | RECURSIVE += $(Y) |
| 27 | Y := 4 |
| 28 | $(warning,RECURSIVE = $(RECURSIVE)) |
| 29 | |
| 30 | # Use += operator to an undefined variable. |
| 31 | # This works as a recursively expanded variable. |
| 32 | Y := 3 |
| 33 | UNDEFINED_VARIABLE += $(Y) |
| 34 | Y := 4 |
| 35 | $(warning,UNDEFINED_VARIABLE = $(UNDEFINED_VARIABLE)) |
| 36 | |
| 37 | # You can use variable references for the lefthand side of assignment statement. |
| 38 | X := A |
| 39 | Y := B |
| 40 | $(X)$(Y) := 5 |
| 41 | $(warning,AB = $(AB)) |
| 42 | |
| 43 | # User-defined function. |
| 44 | greeting = $(1), my name is $(2). |
| 45 | $(warning,$(greeting,Hello,John)) |
| 46 | |
| 47 | # The number of arguments is not checked for user-defined functions. |
| 48 | # If some arguments are optional, it is useful to pass fewer parameters. |
| 49 | # $(2) will be blank in this case. |
| 50 | $(warning,$(greeting,Hello)) |
| 51 | |
| 52 | # Unreferenced parameters are just ignored. |
| 53 | $(warning,$(greeting,Hello,John,ignored,ignored)) |