Add concept exercise: dnd-char / kwdef, using-macros (JuliaLang#381)

* Deprecate v2 exercise dnd-character

There will be a v3 exercise built on this exercise.

* Add concept exercise: dnd-char / kwdef, using-macros

* Add vectors pre-req

Required to understand the examplar solution, and at this point it's very unlikely a student won't have solved it anyway

* Fix exemplar config key

* Apply suggestions from code review

Co-authored-by: Colin Caine <[email protected]>

* Apply more suggestions

Co-authored-by: Colin Caine <[email protected]>

concepts/kwdef/.meta/config.json

@@ -0,0 +1,9 @@
+{
+  "blurb": "The macro `Base.@kwdef` can be used to automatically define constructors that take keyword arguments for type definitions.",
+  "authors": [
+    "SaschaMann"
+  ],
+  "contributors": [
+    "cmcaine"
+  ]
+}

concepts/kwdef/about.md

@@ -0,0 +1,133 @@
+# About
+
+The macro `Base.@kwdef` can be used to automatically define constructors that take keyword arguments for the definition of a [struct][struct].
+These keyword argument constructors can also set default values for fields.
+
+For example, the following definition
+
+```julia
+Base.@kwdef struct HumanStats
+    birthyear::Int
+    height::Int
+    mass::Int
+    bmi::Float64 = mass / (0.01 * height)^2
+end
+```
+
+defines three constructors at once
+
+```julia
+julia> methods(HumanStats)
+# 3 methods for type constructor:
+[1] HumanStats(; birthyear, height, mass, bmi) [...]
+[2] HumanStats(birthyear::Int64, height::Int64, mass::Int64, bmi::Float64) [...]
+[3] HumanStats(birthyear, height, mass, bmi) [...]
+```
+
+including a constructor based on keyword arguments
+
+```julia
+julia> HumanStats(
+           birthyear = 2002,
+           height = 193,
+           mass = 83
+       )
+HumanStats(2002, 193, 83, 22.28247738194314)
+```
+
+whereas the standard definition
+
+```julia
+struct HumanStats
+    birthyear::Int
+    height::Int
+    mass::Int
+    bmi::Float64
+end
+```
+
+only defines the following two
+
+```julia
+julia> methods(HumanStats)
+# 2 methods for type constructor:
+[1] HumanStats(birthyear::Int64, height::Int64, mass::Int64, bmi::Float64) [...]
+[2] HumanStats(birthyear, height, mass, bmi) [...]
+```
+
+and would require manually defining a keyword-based constructor if you wanted one.
+
+## When to use `Base.@kwdef`?
+
+Keyword-based constructors are particularly useful for constructing structs that take a large number of arguments, in particular when the type or value of the arguments don't directly relate to the arguments' meanings.
+
+Consider the following definition:
+
+```julia
+dirk = BasketballPlayer(1978, 1994, 2019, 213, 111, 42, 1998, [2011], 31560, 11489, 3651)
+```
+
+It is not clear what each value means without knowing the definition of the type.
+And even in case one knows the definition, one would probably have to look up the order over and over again.
+
+However, when using a keyboard-based constructor, their meaning is immediately obvious:
+
+```julia
+dirk = BasketballPlayer(
+    birthyear = 1978,
+    career_start = 1994,
+    career_end = 2019,
+    height = 213,
+    weight = 111,
+    number = 42,
+    drafted = 1998,
+    championships = [2011],
+    points = 31560,
+    rebounds = 11489,
+    assists = 3651
+)
+```
+
+<!-- The following type definition was used for the examples above:
+```julia
+struct BasketballPlayer
+    birthyear::Int
+    career_start::Int
+    career_end::Int
+    height::Int
+    weight::Int
+    number::Int
+    drafted::Int
+    championships::Vector{Int}
+    points::Int
+    rebounds::Int
+    assists::Int
+end
+```
+-->
+
+<!-- TODO Maybe mention named tuples as an alternative? -->
+
+~~~~exercism/caution
+`Base.@kwdef` is not exported and not documented in the manual, and therefore not part of [Julia's public API][public-api].
+This means its interface is technically not guaranteed to be stable and may change between minor Julia updates.
+
+However, the macro is widely used across the ecosystem, and it's unlikely that it will be changed in a breaking way.
+
+For more information, see:
+
+- ["What does `@kwdef` do?"][discourse-kwdef]
+- [Julia Issue #32659 to add `@kwdef` to the Manual][add-kwdef-to-manual]
+- [Julia Issue #33192 to export `@kwdef`][export-kwdef]
+
+~~~~
+
+## Sources
+
+1. Dirk Nowitzki, Wikipedia. (2021). https://en.wikipedia.org/w/index.php?title=Dirk_Nowitzki&oldid=1019583359 (accessed April 24, 2021).
+
+[struct]: https://exercism.io/tracks/julia/concepts/structs
+[discourse-kwdef]: https://discourse.julialang.org/t/what-does-kwdef-do/51973/2
+[public-api]: https://github.com/JuliaLang/julia/pull/35715/files#diff-3591da1fafe13d9fcae96e5b32a9492c6fb68b7e33ac0810b106b09b45d59534
+[add-kwdef-to-manual]: https://github.com/JuliaLang/julia/issues/32659
+[export-kwdef]: https://github.com/JuliaLang/julia/issues/33192

concepts/kwdef/introduction.md

@@ -0,0 +1,132 @@
+# Introduction
+
+The macro `Base.@kwdef` can be used to automatically define constructors that take keyword arguments for the definition of a [struct][struct].
+It also allows one to set default values for fields.
+
+For example, the following definition
+
+```julia
+Base.@kwdef struct HumanStats
+    birthyear::Int
+    height::Int
+    mass::Int
+    bmi::Float64 = mass / (0.01 * height)^2
+end
+```
+
+defines three constructors at once
+
+```julia
+julia> methods(HumanStats)
+# 3 methods for type constructor:
+[1] HumanStats(; birthyear, height, mass, bmi) [...]
+[2] HumanStats(birthyear::Int64, height::Int64, mass::Int64, bmi::Float64) [...]
+[3] HumanStats(birthyear, height, mass, bmi) [...]
+```
+
+including a constructor based on keyword arguments
+
+```julia
+julia> HumanStats(
+           birthyear = 2002,
+           height = 193,
+           mass = 83
+       )
+HumanStats(2002, 193, 83, 22.28247738194314)
+```
+
+whereas the standard definition
+
+```julia
+struct HumanStats
+    birthyear::Int
+    height::Int
+    mass::Int
+    bmi::Float64
+end
+```
+
+only defines the following two
+
+```julia
+julia> methods(HumanStats)
+# 2 methods for type constructor:
+[1] HumanStats(birthyear::Int64, height::Int64, mass::Int64, bmi::Float64) [...]
+[2] HumanStats(birthyear, height, mass, bmi) [...]
+```
+
+and would require manually defining a keyword-based constructor.
+
+## When to use `Base.@kwdef`?
+
+Keyword-based constructors are particularly useful for constructing structs that take a large number of arguments, in particular when the type or value of the arguments don't directly relate to the arguments' meanings.
+
+Consider the following definition:
+
+```julia
+dirk = BasketballPlayer(1978, 1994, 2019, 213, 111, 42, 1998, [2011], 31560, 11489, 3651)
+```
+
+It is not clear what each value means without knowing the definition of the type.
+And even in case one knows the definition, one would probably have to look up the order over and over again.
+
+However, when using a keyboard-based constructor, their meaning is immediately obvious:
+
+```julia
+dirk = BasketballPlayer(
+    birthyear = 1978,
+    career_start = 1994,
+    career_end = 2019,
+    height = 213,
+    weight = 111,
+    number = 42,
+    drafted = 1998,
+    championships = [2011],
+    points = 31560,
+    rebounds = 11489,
+    assists = 3651
+)
+```
+
+<!-- The following type definition was used for the examples above:
+```julia
+struct BasketballPlayer
+    birthyear::Int
+    career_start::Int
+    career_end::Int
+    height::Int
+    weight::Int
+    number::Int
+    drafted::Int
+    championships::Vector{Int}
+    points::Int
+    rebounds::Int
+    assists::Int
+end
+```
+-->
+
+~~~~exercism/caution
+`Base.@kwdef` is not exported and not documented in the manual, and therefore not part of [Julia's public API][public-api].
+This means its interface is technically not guaranteed to be stable and may change between minor Julia updates.
+
+However, the macro is widely used across the ecosystem, and it's unlikely that it will be changed in a breaking way.
+
+For more information, see:
+
+- ["What does `@kwdef` do?"][discourse-kwdef]
+- [Julia Issue #32659 to add `@kwdef` to the Manual][add-kwdef-to-manual]
+- [Julia Issue #33192 to export `@kwdef`][export-kwdef]
+
+~~~~
+
+## Sources
+
+1. Dirk Nowitzki, Wikipedia. (2021). https://en.wikipedia.org/w/index.php?title=Dirk_Nowitzki&oldid=1019583359 (accessed April 24, 2021).
+
+
+[struct]: https://exercism.io/tracks/julia/concepts/structs
+[discourse-kwdef]: https://discourse.julialang.org/t/what-does-kwdef-do/51973/2
+[public-api]: https://github.com/JuliaLang/julia/pull/35715/files#diff-3591da1fafe13d9fcae96e5b32a9492c6fb68b7e33ac0810b106b09b45d59534
+[add-kwdef-to-manual]: https://github.com/JuliaLang/julia/issues/32659
+[export-kwdef]: https://github.com/JuliaLang/julia/issues/33192

concepts/kwdef/links.json

@@ -0,0 +1,18 @@
+[
+    {
+        "description": "What does `@kwdef` do?",
+        "url": "https://discourse.julialang.org/t/what-does-kwdef-do/51973/2"
+    },
+    {
+        "description": "Julia Issue #32659 to add `@kwdef` to the Manual",
+        "url": "https://github.com/JuliaLang/julia/issues/32659"
+    },
+    {
+        "description": "Julia Issue #33192 to export `@kwdef`",
+        "url": "https://github.com/JuliaLang/julia/issues/33192"
+    },
+    {
+        "url": "https://github.com/JuliaLang/julia/pull/35715/files#diff-3591da1fafe13d9fcae96e5b32a9492c6fb68b7e33ac0810b106b09b45d59534",
+        "description": "Julia's Public API"
+    }
+]

config.json

@@ -79,6 +79,22 @@
         ],
         "status": "wip"
       },
+      {
+        "uuid": "60e480e9-7f6f-460a-b753-f333a37d3e0c",
+        "name": "DND Character",
+        "slug": "dnd-char",
+        "concepts": [
+          "kwdef",
+          "using-macros"
+        ],
+        "prerequisites": [
+          "immutable-structs",
+          "vectors",
+          "randomness",
+          "keyword-arguments"
+        ],
+        "status": "wip"
+      },
       {
         "uuid": "f2f696e6-8a6a-4c8c-ae0b-d940d8579905",
         "slug": "leap",
@@ -737,7 +753,8 @@
           "randomness",
           "math",
           "test_driven_development"
-        ]
+        ],
+        "status": "deprecated"
       },
       {
         "slug": "robot-simulator",