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49 lines
1.2 KiB
Nim
49 lines
1.2 KiB
Nim
#
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#
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# Nim's Runtime Library
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# (c) Copyright 2020 Andreas Rumpf
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#
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# See the file "copying.txt", included in this
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# distribution, for details about the copyright.
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#
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## This module implements the `with` macro for easy
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## function chaining. See https://github.com/nim-lang/RFCs/issues/193
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## and https://github.com/nim-lang/RFCs/issues/192 for details leading to this
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## particular design.
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##
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## **Since:** version 1.2.
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import macros, private / underscored_calls
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macro with*(arg: typed; calls: varargs[untyped]): untyped =
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## This macro provides `chaining`:idx: of function calls.
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## It does so by patching every call in `calls` to
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## use `arg` as the first argument.
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##
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## .. caution:: This evaluates `arg` multiple times!
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runnableExamples:
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var x = "yay"
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with x:
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add "abc"
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add "efg"
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doAssert x == "yayabcefg"
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var a = 44
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with a:
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+= 4
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-= 5
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doAssert a == 43
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# Nesting works for object types too!
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var foo = (bar: 1, qux: (baz: 2))
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with foo:
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bar = 2
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with qux:
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baz = 3
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doAssert foo.bar == 2
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doAssert foo.qux.baz == 3
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result = newNimNode(nnkStmtList, arg)
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underscoredCalls(result, calls, arg)
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