Make some improvements to the Scoped Values documentation. (#53628)

Fixes #53471.

One thing to note, I changed the signature in the `with` docstring from
this:

```julia
with(f, (var::ScopedValue{T} => val::T)...)
```

to this:

```julia
with(f, (var::ScopedValue{T} => val)...)
```

...since the original signature in the docstring was too strict. I also
added this sentence to the docstring:

```julia
`val` will be converted to type `T`.
```

I added a couple tests that verify the conversion behavior.

(cherry picked from commit 7613c69)

base/scopedvalues.jl

@@ -3,6 +3,7 @@
 module ScopedValues
 
 export ScopedValue, with, @with
+public get
 
 """
     ScopedValue(x)
@@ -54,7 +55,22 @@ Base.eltype(::ScopedValue{T}) where {T} = T
 """
     isassigned(val::ScopedValue)
 
-Test whether a ScopedValue has an assigned value.
+Test whether a `ScopedValue` has an assigned value.
+
+See also: [`ScopedValues.with`](@ref), [`ScopedValues.@with`](@ref), [`ScopedValues.get`](@ref).
+
+# Examples
+```jldoctest
+julia> using Base.ScopedValues
+
+julia> a = ScopedValue(1); b = ScopedValue{Int}();
+
+julia> isassigned(a)
+true
+
+julia> isassigned(b)
+false
+```
 """
 function Base.isassigned(val::ScopedValue)
     val.has_default && return true
@@ -114,6 +130,21 @@ const novalue = NoValue()
 If the scoped value isn't set and doesn't have a default value,
 return `nothing`. Otherwise returns `Some{T}` with the current
 value.
+
+See also: [`ScopedValues.with`](@ref), [`ScopedValues.@with`](@ref), [`ScopedValues.ScopedValue`](@ref).
+
+# Examples
+```jldoctest
+julia> using Base.ScopedValues
+
+julia> a = ScopedValue(42); b = ScopedValue{Int}();
+
+julia> ScopedValues.get(a)
+Some(42)
+
+julia> isnothing(ScopedValues.get(b))
+true
+```
 """
 function get(val::ScopedValue{T}) where {T}
     scope = Core.current_scope()::Union{Scope, Nothing}
@@ -151,11 +182,32 @@ function Base.show(io::IO, val::ScopedValue)
 end
 
 """
-    @with vars... expr
+    @with (var::ScopedValue{T} => val)... expr
+
+Macro version of `with`. The expression `@with var=>val expr` evaluates `expr` in a
+new dynamic scope with `var` set to `val`. `val` will be converted to type `T`.
+`@with var=>val expr` is equivalent to `with(var=>val) do expr end`, but `@with`
+avoids creating a closure.
+
+See also: [`ScopedValues.with`](@ref), [`ScopedValues.ScopedValue`](@ref), [`ScopedValues.get`](@ref).
+
+# Examples
+```jldoctest
+julia> using Base.ScopedValues
 
-Macro version of `with(f, vars...)` but with `expr` instead of `f` function.
-This is similar to using [`with`](@ref) with a `do` block, but avoids creating
-a closure.
+julia> const a = ScopedValue(1);
+
+julia> f(x) = a[] + x;
+
+julia> @with a=>2 f(10)
+12
+
+julia> @with a=>3 begin
+           x = 100
+           f(x)
+       end
+103
+```
 """
 macro with(exprs...)
     if length(exprs) > 1
@@ -172,9 +224,44 @@ macro with(exprs...)
 end
 
 """
-    with(f, (var::ScopedValue{T} => val::T)...)
+    with(f, (var::ScopedValue{T} => val)...)
+
+Execute `f` in a new dynamic scope with `var` set to `val`. `val` will be converted
+to type `T`.
+
+See also: [`ScopedValues.@with`](@ref), [`ScopedValues.ScopedValue`](@ref), [`ScopedValues.get`](@ref).
+
+# Examples
+```jldoctest
+julia> using Base.ScopedValues
+
+julia> a = ScopedValue(1);
 
-Execute `f` in a new scope with `var` set to `val`.
+julia> f(x) = a[] + x;
+
+julia> f(10)
+11
+
+julia> with(a=>2) do
+           f(10)
+       end
+12
+
+julia> f(10)
+11
+
+julia> b = ScopedValue(2);
+
+julia> g(x) = a[] + b[] + x;
+
+julia> with(a=>10, b=>20) do
+           g(30)
+       end
+60
+
+julia> with(() -> a[] * b[], a=>3, b=>4)
+12
+```
 """
 function with(f, pair::Pair{<:ScopedValue}, rest::Pair{<:ScopedValue}...)
     @with(pair, rest..., f())

doc/src/base/scopedvalues.md

@@ -17,18 +17,15 @@ concurrently.
     Scoped values were introduced in Julia 1.11. In Julia 1.8+ a compatible
     implementation is available from the package ScopedValues.jl.
 
-In its simplest form you can create a [`Base.ScopedValue`](@ref) with a
-default value and then use [`Base.with`](@ref with) or [`Base.@with`](@ref) to
-enter a new dynamic scope.
+In its simplest form you can create a [`ScopedValue`](@ref Base.ScopedValues.ScopedValue)
+with a default value and then use [`with`](@ref Base.ScopedValues.with) or
+[`@with`](@ref Base.ScopedValues.@with) to enter a new dynamic scope. The new scope will
+inherit all values from the parent scope (and recursively from all outer scopes) with the
+provided scoped value taking priority over previous definitions.
 
-The new scope will inherit all values from the parent scope
-(and recursively from all outer scopes) with the provided scoped
-value taking priority over previous definitions.
-
-Let's first look at an example of **lexical** scope:
-
-A `let` statements begins a new lexical scope within which the outer definition
-of `x` is shadowed by it's inner definition.
+Let's first look at an example of **lexical** scope. A `let` statement begins
+a new lexical scope within which the outer definition of `x` is shadowed by
+it's inner definition.
 
 ```julia
 x = 1
@@ -38,9 +35,9 @@ end
 @show x # 1
 ```
 
-Since Julia uses lexical scope the variable `x` is bound within the function `f`
-to the global scope and entering a `let` scope does not change the value `f`
-observes.
+In the following example, since Julia uses lexical scope, the variable `x` in the body
+of `f` refers to the `x` defined in the global scope, and entering a `let` scope does
+not change the value `f` observes.
 
 ```julia
 x = 1
@@ -64,7 +61,7 @@ end
 f() # 1
 ```
 
-Not that the observed value of the `ScopedValue` is dependent on the execution
+Note that the observed value of the `ScopedValue` is dependent on the execution
 path of the program.
 
 It often makes sense to use a `const` variable to point to a scoped value,
@@ -74,34 +71,54 @@ and you can set the value of multiple `ScopedValue`s with one call to `with`.
 ```julia
 using Base.ScopedValues
 
-const scoped_val = ScopedValue(1)
-const scoped_val2 = ScopedValue(0)
-
-# Enter a new dynamic scope and set value
-@show scoped_val[] # 1
-@show scoped_val2[] # 0
-with(scoped_val => 2) do
-    @show scoped_val[] # 2
-    @show scoped_val2[] # 0
-    with(scoped_val => 3, scoped_val2 => 5) do
-        @show scoped_val[] # 3
-        @show scoped_val2[] # 5
+f() = @show a[]
+g() = @show b[]
+
+const a = ScopedValue(1)
+const b = ScopedValue(2)
+
+f() # a[] = 1
+g() # b[] = 2
+
+# Enter a new dynamic scope and set value.
+with(a => 3) do
+    f() # a[] = 3
+    g() # b[] = 2
+    with(a => 4, b => 5) do
+        f() # a[] = 4
+        g() # b[] = 5
     end
-    @show scoped_val[] # 2
-    @show scoped_val2[] # 0
+    f() # a[] = 3
+    g() # b[] = 2
 end
-@show scoped_val[] # 1
-@show scoped_val2[] # 0
+
+f() # a[] = 1
+g() # b[] = 2
 ```
 
-Since `with` requires a closure or a function and creates another call-frame,
-it can sometimes be beneficial to use the macro form.
+`ScopedValues` provides a macro version of `with`. The expression `@with var=>val expr`
+evaluates `expr` in a new dynamic scope with `var` set to `val`. `@with var=>val expr`
+is equivalent to `with(var=>val) do expr end`. However, `with` requires a zero-argument
+closure or function, which results in an extra call-frame. As an example, consider the
+following function `f`:
 
 ```julia
 using Base.ScopedValues
+const a = ScopedValue(1)
+f(x) = a[] + x
+```
+
+If you wish to run `f` in a dynamic scope with `a` set to `2`, then you can use `with`:
 
-const STATE = ScopedValue{State}()
-with_state(f, state::State) = @with(STATE => state, f())
+```julia
+with(() -> f(10), a=>2)
+```
+
+However, this requires wrapping `f` in a zero-argument function. If you wish to avoid
+the extra call-frame, then you can use the `@with` macro:
+
+```julia
+@with a=>2 f(10)
 ```
 
 !!! note
@@ -265,11 +282,11 @@ Base.@kwdef struct Configuration
     verbose::Bool = false
 end
 
-const CONFIG = ScopedValue(Configuration())
+const CONFIG = ScopedValue(Configuration(color=true))
 
-@with CONFIG => Configuration(CONFIG[], color=true) begin
+@with CONFIG => Configuration(color=CONFIG[].color, verbose=true) begin
     @show CONFIG[].color # true
-    @show CONFIG[].verbose # false
+    @show CONFIG[].verbose # true
 end
 ```
 

test/scopedvalues.jl

@@ -52,6 +52,16 @@ emptyf() = nothing
 @testset "conversion" begin
     with(emptyf, sval_float=>2)
     @test_throws MethodError with(emptyf, sval_float=>"hello")
+    a = ScopedValue(1)
+    with(a => 2.0) do
+        @test a[] == 2
+        @test a[] isa Int
+    end
+    a = ScopedValue(1.0)
+    with(a => 2) do
+        @test a[] == 2.0
+        @test a[] isa Float64
+    end
 end
 
 import Base.Threads: @spawn