refactor(bvar): expand metric constructor macro

[darion-yaphet]

Summary

• Remove the COMMON_VARIABLE_CONSTRUCTOR macro
• Replace its uses in the Babylon counter variants of Adder, Maxer, Miner, and IntRecorder with explicit constructors
• Preserve the existing constructor behavior for default construction, expose(name), and expose_as(prefix, name)

Motivation

COMMON_VARIABLE_CONSTRUCTOR hid public constructors behind macro expansion, making the code harder to read, search, and navigate with regular C++ tooling.

This change keeps the API behavior unchanged while making the constructors visible at their declaration sites.

using Base::Base was intentionally avoided because it would expose additional internal base constructors in the Babylon counter path and could broaden the public
API.

Testing

• cmake --build build --target brpc-static -j6
• git diff --check
• rg COMMON_VARIABLE_CONSTRUCTOR . -g '!build/**'

Notes

The WITH_BABYLON_COUNTER path was not compiled locally because the available Bazel setup is missing the repository-required Bazel 7.2.1 binary.

[chenBright]

I think this is to simplify the code, which is fine, like the DISALLOW_COPY_AND_ASSIGN macro.

[Copilot]

Pull request overview

This PR refactors the bvar public headers by removing the COMMON_VARIABLE_CONSTRUCTOR macro and expanding its usages into explicit, readable constructors (primarily for the WITH_BABYLON_COUNTER specializations). The intent is to preserve the existing construction behavior (default, expose(name), expose_as(prefix, name)) while improving navigability and searchability in C++ tooling.

Changes:

• Removed COMMON_VARIABLE_CONSTRUCTOR from bvar/variable.h.
• Replaced macro usage with explicit constructors in Adder, Maxer, and Miner Babylon-counter specializations.
• Replaced macro usage with explicit constructors in the Babylon-counter IntRecorder variant.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/bvar/variable.h	Removes the shared constructor macro from a publicly installed bvar header.
src/bvar/reducer.h	Expands the macro into explicit constructors for Babylon-counter Adder/Maxer/Miner.
src/bvar/recorder.h	Expands the macro into explicit constructors for the Babylon-counter IntRecorder.

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[wwbmmm]

I think this is to simplify the code, which is fine, like the DISALLOW_COPY_AND_ASSIGN macro.

Agree

[darion-yaphet]

I think this is to simplify the code, which is fine, like the DISALLOW_COPY_AND_ASSIGN macro.

Agree

I agree the macro reduces a few lines, but it hides public constructors, which are part of the API surface and important for readability/tooling. Since these constructors are simple and type-specific, spelling them out makes the public interface clearer.

That said, because variable.h is installed as a public header, removing the macro may break downstream users. I can keep a deprecated compatibility definition for one release while removing internal usages, then remove it in a later breaking-change cycle.