This library is an experiment, and comes with heavier compilation times, a basic benchmark is provided at the end of this file.
I recommend NOT to use it in a production environment.
A macro for object construction using {} (curlies).
With curlies, initialization of required fields is checked at compile-time. For object fields with a default value (available since nim 2.0), initialization is obviously not mandatory.
It's simply a macro equivalent for the common proc init[T](_: type T, ...)
that uses the type's declaration to dispatch and check all required fields
are provided.
The output of a curlies construction is an object construction expression,
no temporary variables are introduced.
I wanted to get a better grasp of nim's macro system and see how far it could be pushed to enable static checks on missing fields for object initialization.
Install curlies with nimble:
$ nimble install curlies
Alternatively, curlies can be installed with atlas:
$ atlas use curlies
Curlies is defined as a typed macro:
macro `{}`*(T: typedesc, params: varargs[untyped]): untypedIt's somehow similar to rust's struct initialization syntax, the main difference
being you cannot use a whitespace between the type and opening bracket {.
Borrowed features include:
type
MyType = object
myField: int
let
myField = 1
full = MyType{ myField: myField }
short = MyType{ myField }
assert full == shorttype
MyType = object
a, b, c: int
let
original = MyType(a: 1, b: 2, c: 3)
derived = MyType{ a: 4, ..original }
assert derived == MyType(a: 4, b: 2, c: 3)Most nim types should work out of the box, tests currently cover:
- objects
- ref objects
- generic objects
- distinct objects
- variant objects
- inheritance objects
- tuples
- even fungus ADTs!
Curlies behaviour differs based on the module where it is used.
- for types declared in the same module, all non-default fields are enforced.
- for types declared in another module, only exported fields are enforced, unless of course they bring a default value.
type
Person = object
name: string
age, height: int
favouriteNumber: int = 3
const
alice = Person{
name: "Alice",
age: 30,
height: 175
}
echo alice
# (name: "Alice", age: 30, height: 175, favouriteNumber: 3)type
Person = object
name: string
age, height: int
favouriteNumber: int = 3
let
name = "Bob"
height = 155
bob = Person{
name,
height,
..alice,
}
echo bob
# (name: "Bob", age: 30, height: 155, favouriteNumber: 3)type
Person = object
name: string
age, height: int
favouriteNumber: int = 3
echo Person{ name: "Incomplete" }
# Error: @[age, height]: initialization required.I compared compiling tests/tbasic.nim with its equivalent that uses regular
object construction tests/tbasic_nocurlies.nim, numbers below:
- With latest stable
$ nim -v
Nim Compiler Version 2.0.2 [Linux: amd64]
Compiled at 2023-12-15
Copyright (c) 2006-2023 by Andreas Rumpf
git hash: c4c44d10df8a14204a75c34e499def200589cb7c
active boot switches: -d:release
$ hyperfine \
'nim c -f --hints:off -o:/tmp/tbasic tests/tbasic.nim' \
'nim c -f --hints:off -o:/tmp/tbasic tests/tbasic_nocurlies.nim'
Benchmark 1: nim c -f --hints:off -o:/tmp/tbasic tests/tbasic.nim
Time (mean ± σ): 1.707 s ± 0.051 s [User: 3.175 s, System: 0.706 s]
Range (min … max): 1.652 s … 1.799 s 10 runs
Benchmark 2: nim c -f --hints:off -o:/tmp/tbasic tests/tbasic_nocurlies.nim
Time (mean ± σ): 1.557 s ± 0.031 s [User: 3.003 s, System: 0.699 s]
Range (min … max): 1.505 s … 1.587 s 10 runs
Summary
nim c -f --hints:off -o:/tmp/tbasic tests/tbasic_nocurlies.nim ran
1.10 ± 0.04 times faster than nim c -f --hints:off -o:/tmp/tbasic tests/tbasic.nim- With latest devel
$ nim -v
Nim Compiler Version 2.1.1 [Linux: amd64]
Compiled at 2024-01-14
Copyright (c) 2006-2024 by Andreas Rumpf
git hash: ab4278d2179639f19967431a7aa1be858046f7a7
active boot switches: -d:release
$ hyperfine \
'nim c -f --hints:off -o:/tmp/tbasic tests/tbasic.nim' \
'nim c -f --hints:off -o:/tmp/tbasic tests/tbasic_nocurlies.nim'
Benchmark 1: nim c -f --hints:off -o:/tmp/tbasic tests/tbasic.nim
Time (mean ± σ): 2.805 s ± 0.271 s [User: 5.384 s, System: 2.553 s]
Range (min … max): 2.447 s … 3.368 s 10 runs
Benchmark 2: nim c -f --hints:off -o:/tmp/tbasic tests/tbasic_nocurlies.nim
Time (mean ± σ): 2.252 s ± 0.230 s [User: 4.615 s, System: 1.920 s]
Range (min … max): 2.061 s … 2.741 s 10 runs
Summary
nim c -f --hints:off -o:/tmp/tbasic tests/tbasic_nocurlies.nim ran
1.25 ± 0.18 times faster than nim c -f --hints:off -o:/tmp/tbasic tests/tbasic.nimOn my computer, curlies comes with 10 to 25% slower compilation, depending on the compiler version.
Well this is an experiment anyway, I must advise against using it in a production environment.
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