Add @pack! and @pack_fields! (#4)

* Add `@pack!` and `@pack_fields!`

* Simplify file structure

* A few initial tests

* Fix macros and add more tests

Project.toml

@@ -1,7 +1,7 @@
 name = "SimpleUnPack"
 uuid = "ce78b400-467f-4804-87d8-8f486da07d0a"
 authors = ["David Widmann"]
-version = "1.0.1"
+version = "1.1.0"
 
 [compat]
 julia = "1"

README.md

@@ -4,8 +4,16 @@
 [![Coverage](https://codecov.io/gh/devmotion/SimpleUnPack.jl/branch/main/graph/badge.svg)](https://codecov.io/gh/devmotion/SimpleUnPack.jl)
 [![Code Style: Blue](https://img.shields.io/badge/code%20style-blue-4495d1.svg)](https://github.com/invenia/BlueStyle)
 
-This package provides the `@unpack` and `@unpack_fields` macros for destructuring properties and fields, respectively.
-The behaviour of `@unpack` is equivalent to the destructuring that was introduced in [Julia#39285](https://github.com/JuliaLang/julia/pull/39285) and is available in Julia >= 1.7.0-DEV.364.
+This package provides four macros, namely
+
+- `@unpack` for destructuring properties,
+- `@pack!` for setting properties,
+- `@unpack_fields` for destructuring fields,
+- `@pack_fields!` for setting fields.
+
+`@unpack`/`@pack!` are based on `getproperty`/`setproperty` whereas `@unpack_fields`/`@pack_fields!` are based on `getfield`/`setfield!`.
+
+In Julia >= 1.7.0-DEV.364, `@unpack` is expanded to the destructuring syntax that was introduced in [Julia#39285](https://github.com/JuliaLang/julia/pull/39285).
 
 ## Examples
 
@@ -40,7 +48,7 @@ An example with a custom struct in a function:
 ```julia
 julia> using SimpleUnPack
 
-julia> struct MyStruct{X,Y}
+julia> mutable struct MyStruct{X,Y}
            x::X
            y::Y
        end
@@ -55,6 +63,14 @@ julia> function Base.getproperty(m::MyStruct, p::Symbol)
            end
        end
 
+julia> function Base.setproperty!(m::MyStruct, p::Symbol, v)
+           if p === :y
+               setfield!(m, p, 2 * v)
+           else
+               setfield!(m, p, v)
+           end
+       end
+
 julia> function g(m::MyStruct)
            @unpack x, y = m
            return (; x, y)
@@ -63,22 +79,37 @@ julia> function g(m::MyStruct)
 julia> g(MyStruct(1.0, -5))
 (x = 1.0, y = 42)
 
+julia> function g!(m::MyStruct, x, y)
+          @pack! m = x, y
+          return m
+       end;
+
+julia> g!(MyStruct(2.1, 5), 1.2, 2)
+MyStruct{Float64, Int64}(1.2, 4)
+
 julia> function h(m::MyStruct)
            @unpack_fields x, y = m
            return (; x, y)
        end
 
 julia> h(MyStruct(1.0, -5))
 (x = 1.0, y = -5)
+
+julia> function h!(m::MyStruct, x, y)
+          @pack_fields! m = x, y
+          return m
+       end;
+
+julia> h!(MyStruct(2.1, 5), 1.2, 2)
+MyStruct{Float64, Int64}(1.2, 2)
 ```
 
 ## Comparison with UnPack.jl
 
-The syntax of `@unpack` is based on [`UnPack.@unpack`](https://github.com/mauro3/UnPack.jl).
-However, `UnPack.@unpack` is more flexible and based on `UnPack.unpack` instad of `getproperty`.
-While `UnPack.unpack` falls back to `getproperty`, it also supports `AbstractDict`s with keys of type `Symbol` and `AbstractString`, and can be specialized for other types.
-Since `UnPack.unpack` dispatches on `Val(property)` instances, this increased flexibility comes at the cost of increased compilation times.
+The syntax of `@unpack` and `@pack!` is based on `UnPack.@unpack` and `UnPack.@pack!` in [UnPack.jl](https://github.com/mauro3/UnPack.jl).
 
-In contrast to SimpleUnPack, UnPack provides an `UnPack.@pack!` macro for setting properties.
+`UnPack.@unpack`/`UnPack.@pack!` are more flexible since they are based on `UnPack.unpack`/`UnPack.pack!` instad of `getproperty`/`setproperty!`.
+While `UnPack.unpack`/`UnPack.pack!` fall back to `getproperty`/`setproperty!`, they also support `AbstractDict`s with keys of type `Symbol` and `AbstractString` and can be specialized for other types.
+Since `UnPack.unpack` and `UnPack.pack!` dispatch on `Val(property)` instances, this increased flexibility comes at the cost of increased number of specializations and increased compilation times.
 
-However, currently UnPack does not support destructuring based on `getfield` only ([UnPack#23](https://github.com/mauro3/UnPack.jl/issues/23)).
+In contrast to SimpleUnPack, currently UnPack does not support destructuring/updating based on `getfield`/`setfield!` only ([UnPack#23](https://github.com/mauro3/UnPack.jl/issues/23)).

src/SimpleUnPack.jl

@@ -1,6 +1,6 @@
 module SimpleUnPack
 
-export @unpack, @unpack_fields
+export @unpack, @unpack_fields, @pack!, @pack_fields!
 
 """
     @unpack a, b, ... = x
@@ -9,93 +9,173 @@ Destructure properties `a`, `b`, ... of `x` into variables of the same name.
 
 The behaviour of the macro is equivalent to `(; a, b, ...) = x` which was introduced in [Julia#39285](https://github.com/JuliaLang/julia/pull/39285) and is available in Julia >= 1.7.0-DEV.364.
 
-See also [`@unpack_fields`](@ref)
+See also [`@pack!`](@ref), [`@unpack_fields`](@ref), [`@pack_fields!`](@ref)
 """
 macro unpack(args)
-    # Extract names of properties and RHS
-    names, rhs = split_names_rhs(:unpack, args)
+    # Extract names of properties and object
+    names, object = split_names_object(:unpack, args, true)
 
     # Construct destructuring expression
     expr = if VERSION >= v"1.7.0-DEV.364"
         # Fall back to destructuring in Base when available:
         # https://github.com/JuliaLang/julia/pull/39285
-        Expr(:(=), Expr(:tuple, Expr(:parameters, (esc(p) for p in names)...)), esc(rhs))
+        Expr(:(=), Expr(:tuple, Expr(:parameters, (esc(p) for p in names)...)), esc(object))
     else
-        destructuring_expr(:getproperty, names, rhs)
+        destructuring_expr(:getproperty, names, object)
     end
 
     return expr
 end
 
+"""
+    @pack! x = a, b, ...
+
+Set properties `a`, `b`, ... of `x` to the given values.
+
+See also [`@unpack`](@ref), [`@unpack_fields`](@ref), [`@pack_fields!`](@ref)
+"""
+macro pack!(args)
+    # Extract names of properties and the object that will be updated
+    names, object = split_names_object(:pack!, args, false)
+
+    # Construct updating expression
+    expr = updating_expr(:setproperty!, object, names)
+
+    return expr
+end
+
 """
     @unpack_fields a, b, ... = x
 
 Destructure fields `a`, `b`, ... of `x` into variables of the same name.
 
-See also [`@unpack`](@ref)
+See also [`@pack_fields!`](@ref), [`@unpack`](@ref), [`@pack!`](@ref)
 """
 macro unpack_fields(args)
-    # Extract names of fields and RHS
-    names, rhs = split_names_rhs(:unpack_fields, args)
+    # Extract names of fields and object
+    names, object = split_names_object(:unpack_fields, args, true)
 
     # Construct destructuring expression
-    expr = destructuring_expr(:getfield, names, rhs)
+    expr = destructuring_expr(:getfield, names, object)
+
+    return expr
+end
+
+"""
+    @pack_fields! x = a, b, ...
+
+Set fields `a`, `b`, ... of `x` to the given values.
+
+See also [`@unpack_fields`](@ref), [`@unpack`](@ref), [`@pack!`](@ref)
+"""
+macro pack_fields!(args)
+    # Extract names of properties and the object that will be updated
+    names, object = split_names_object(:pack_fields!, args, false)
+
+    # Construct updating expression
+    expr = updating_expr(:setfield!, object, names)
 
     return expr
 end
 
 """
-    split_names_rhs(macrosym::Symbol, expr)
+    split_names_object(macrosym::Symbol, expr, object_on_rhs::Bool)
 
-Split an expression `expr` of the form `a, b, ... = x` into a tuple consisting of a vector of symbols `a`, `b`, ..., and the right-hand side `x`.
+Split an expression `expr` of the form `a, b, ... = x` (if `object_on_rhs = true`) or `x = a, b, ...` (if `object_on_rhs = false`) into a tuple consisting of a vector of symbols `a`, `b`, ..., and the expression or symbol for `x`.
 
 The symbol `macro_name` specifies the macro from which this function is called.
 
-This function is used internally with `macrosym = :unpack` and `macrosym = :unpack_fields`.
+This function is used internally with `macrosym = :unpack`, `macrosym = :unpack_fields`, `macrosym = :pack!`, and `macrosym = :pack_fields!`.
 """
-function split_names_rhs(macrosym::Symbol, expr)
+function split_names_object(macrosym::Symbol, expr, object_on_rhs::Bool)
+    # Split expression in LHS and RHS
     if !Meta.isexpr(expr, :(=), 2)
         throw(
             ArgumentError(
-                "`@$macrosym` can only be applied to expressions of the form `a, b, ... = x`",
+                "`@$macrosym` can only be applied to expressions of the form " *
+                (object_on_rhs ? "`a, b, ... = x`" : "`x = a, b, ...`"),
             ),
         )
     end
     lhs, rhs = expr.args
-    names = if lhs isa Symbol
-        [lhs]
-    elseif Meta.isexpr(lhs, :tuple) &&
-        !isempty(lhs.args) &&
-        all(x -> x isa Symbol, lhs.args)
-        lhs.args
+
+    # Clean expression with keys a bit:
+    # Remove line numbers and unwrap it from `:block` expression
+    names_expr = object_on_rhs ? lhs : rhs
+    Base.remove_linenums!(names_expr)
+    if Meta.isexpr(names_expr, :block, 1)
+        names_expr = names_expr.args[1]
+    end
+
+    # Ensure that names are given as symbol or tuple of symbols,
+    # and convert them to a vector of symbols
+    names = if names_expr isa Symbol
+        [names_expr]
+    elseif Meta.isexpr(names_expr, :tuple) &&
+        !isempty(names_expr.args) &&
+        all(x -> x isa Symbol, names_expr.args)
+        names_expr.args
     else
         throw(
             ArgumentError(
-                "`@$macrosym` can only be applied to expressions of the form `a, b, ... = x`",
+                "`@$macrosym` can only be applied to expressions of the form " *
+                (object_on_rhs ? "`a, b, ... = x`" : "`x = a, b, ...`"),
             ),
         )
     end
-    return names, rhs
+
+    # Extract the object
+    object = object_on_rhs ? rhs : lhs
+
+    return names, object
 end
 
 """
-    destructuring_expr(fsym::Symbol, names, rhs)
+    destructuring_expr(fsym::Symbol, names, object)
 
-Return an expression that destructures `rhs` based on a function of name `fsym` and keys `names` into variables of the same `names`.
+Return an expression that destructures `object` based on a function of name `fsym` and keys `names` into variables of the same `names`.
 
 This function is used internally with `fsym = :getproperty` and `fsym = :getfield`.
 """
-function destructuring_expr(fsym::Symbol, names, rhs)
-    @gensym object
+function destructuring_expr(fsym::Symbol, names, object)
+    @gensym instance
     block = Expr(:block)
     for p in names
-        push!(block.args, Expr(:(=), esc(p), Expr(:call, fsym, esc(object), QuoteNode(p))))
+        push!(
+            block.args, Expr(:(=), esc(p), Expr(:call, fsym, esc(instance), QuoteNode(p)))
+        )
     end
     return Base.remove_linenums!(
         quote
-            local $(esc(object)) = $(esc(rhs)) # In case the RHS is an expression
+            local $(esc(instance)) = $(esc(object)) # In case the object is an expression
             $block
-            $(esc(object)) # Return evaluation of the RHS
+            $(esc(instance)) # Return evaluation of the object
+        end,
+    )
+end
+
+"""
+    updating_expr(fsym::Symbol, object, names)
+
+Return an expression that updates keys `names` of `object` with variables of the same `names` based on a function of name `fsym`.
+
+This function is used internally with `fsym = :setproperty!` and `fsym = :setfield!`.
+"""
+function updating_expr(fsym::Symbol, object, names)
+    @gensym instance
+    if length(names) == 1
+        p = first(names)
+        expr = Expr(:call, fsym, esc(instance), QuoteNode(p), esc(p))
+    else
+        expr = Expr(:tuple)
+        for p in names
+            push!(expr.args, Expr(:call, fsym, esc(instance), QuoteNode(p), esc(p)))
+        end
+    end
+    return Base.remove_linenums!(
+        quote
+            local $(esc(instance)) = $(esc(object)) # In case the object is an expression
+            $expr
         end,
     )
 end