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#
#
# Nim's Runtime Library
# (c) Copyright 2020 Andreas Rumpf
#
# See the file "copying.txt", included in this
# distribution, for details about the copyright.
#
## This module implements the ``with`` macro for easy
## function chaining. See https://github.com/nim-lang/RFCs/issues/193
## and https://github.com/nim-lang/RFCs/issues/192 for details leading to this
## particular design.
##
## **Since** version 1.2.
import macros, private / underscored_calls
macro with*(arg: typed; calls: varargs[untyped]): untyped =
## This macro provides the `chaining`:idx: of function calls.
## It does so by patching every call in `calls` to
## use `arg` as the first argument.
## **This evaluates `arg` multiple times!**
runnableExamples:
var x = "yay"
with x:
add "abc"
add "efg"
doAssert x == "yayabcefg"
var a = 44
with a:
+= 4
-= 5
doAssert a == 43
result = newNimNode(nnkStmtList, arg)
underscoredCalls(result, calls, arg)
when isMainModule:
type
Foo = object
col, pos: string
name: string
proc setColor(f: var Foo; r, g, b: int) = f.col = $(r, g, b)
proc setPosition(f: var Foo; x, y: float) = f.pos = $(x, y)
var f: Foo
with(f, setColor(2, 3, 4), setPosition(0.0, 1.0))
echo f
f = Foo()
with f:
col = $(2, 3, 4)
pos = $(0.0, 1.0)
_.name = "bar"
echo f
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