Add ReadList helper

[ViniciusCestarii]

Follow up of #277 (review). This adds ReadList helper and uses it to dedup the CustomReadField implementations for std::map, std::set, std::unordered_set, and std::vector, mirroring the existing BuildList helper on the build side.

I took the liberty of adding the commit f2a734a "type: reserve first when reading std::unordered_set" so it reserves the correct capacity first and then emplaces the values.

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Reviews

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Type	Reviewers
ACK	xyzconstant
Concept ACK	ryanofsky

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #288 (Create support branch for CI scripts, documentation, and examples by ryanofsky)

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[ryanofsky]

Concept ACK f2a734a. Thanks for the followup. Plan to review more after #277 is merged

[ViniciusCestarii]

Forced push 245f792 to just rebase with master

[ViniciusCestarii]

Forced push 5d23f83 applying @ryanofsky suggestion. It reads cleaner and dedup more code.

[xyzconstant]

Does this work here?

diff --git a/include/mp/type-vector.h b/include/mp/type-vector.h
index 25e74a6..cd269cb 100644
--- a/include/mp/type-vector.h
+++ b/include/mp/type-vector.h
@@ -50,14 +50,16 @@ decltype(auto) CustomReadField(TypeList<std::vector<bool>>,
                                Input&& input,
                                ReadDest&& read_dest)
 {
-    return read_dest.update([&](auto& value) {
-        auto data = input.get();
-        value.clear();
-        value.reserve(data.size());
-        for (auto item : data) {
-            value.push_back(ReadField(TypeList<bool>(), invoke_context, Make<ValueField>(item), ReadDestTemp<bool>()));
-        }
-    });
+    return ReadList(
+        TypeList<bool>(), invoke_context, input, read_dest,
+        [&](auto& value, size_t size) {
+            value.clear();
+            value.reserve(size);
+        },
+        [&](auto& value, auto&& item) {
+            value.push_back(item);
+            return value.back();
+        });
 }
 } // namespace mp

[ViniciusCestarii]

oh I missed this case, thanks for pointing!

I tested your approach and it does compile and passes the tests but I think it is better to not add return value.back(); because bool is read via construct(), so the return value is always unused.

Also I think it is a good opportunity to add a comment to explain why there's this exception for std::vector<bool>.

What do you think?

diff --git a/include/mp/type-vector.h b/include/mp/type-vector.h
index 25e74a6..49ca3c2 100644
--- a/include/mp/type-vector.h
+++ b/include/mp/type-vector.h
@@ -43,6 +43,11 @@ decltype(auto) CustomReadField(TypeList<std::vector<LocalType>>,
         });
 }
 
+//! Overload CustomReadField for std::vector<bool>, which needs its own handler
+//! because its back() returns a proxy by value (std::vector<bool>::reference)
+//! rather than a reference, so it can't use the generic vector in-place emplace path
+//! that returns auto&. Not returning a reference is fine here: bool is read via
+//! construct(), not update(), so the return value is never used.
 template <typename Input, typename ReadDest>
 decltype(auto) CustomReadField(TypeList<std::vector<bool>>,
                                Priority<1>,
@@ -50,14 +55,15 @@ decltype(auto) CustomReadField(TypeList<std::vector<bool>>,
                                Input&& input,
                                ReadDest&& read_dest)
 {
-    return read_dest.update([&](auto& value) {
-        auto data = input.get();
-        value.clear();
-        value.reserve(data.size());
-        for (auto item : data) {
-            value.push_back(ReadField(TypeList<bool>(), invoke_context, Make<ValueField>(item), ReadDestTemp<bool>()));
-        }
-    });
+    return ReadList(
+        TypeList<bool>(), invoke_context, input, read_dest,
+        [&](auto& value, size_t size) {
+            value.clear();
+            value.reserve(size);
+        },
+        [&](auto& value, auto&& item) {
+            value.push_back(item);
+        });
 }
 } // namespace mp
 

[xyzconstant]

Great! This is definitely better, and the comment is on point.

[ViniciusCestarii]

Done on 1bfc594.

[ViniciusCestarii]

Forced push 043b8a8 applying @xyzconstant suggestion

[xyzconstant]

tACK 043b8a8

Thanks for the updates @ViniciusCestarii.

This is a simple refactor that moves common code to ReadList, consistent with existing BuildList helper.

The changes are clean and can be merged as-is.