#reflection
24 posts tagged #reflection.
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Reflection across languages: C++26 vs Rust, C#, Java, TypeScript, Go, Python
Capstone: the canonical reflection tasks — serialize, enum↔string, CLI parsing, ORM row binding — side by side in seven mainstream languages. Where C++ lands, and what the uniquely-C++ angle actually gives you.
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Replacing Qt's MOC with reflection
Qt's Meta-Object Compiler parses Q_OBJECT/Q_PROPERTY declarations and emits glue code. With C++26 reflection, Q_PROPERTY-equivalent becomes a library pattern — no external compiler, no generated files.
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The fastest JVM is the C++26 compiler
Koen Samyn's BeCPP talk used std::meta::substitute to transform Java bytecode into executable C++ at compile time. The compiler constant-folds the entire program. The loop doesn't run faster. It doesn't exist. This is reflection used not for serialization or enum-to-string, but as a compile-time metaprogramming substrate for building language interpreters.
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define_aggregate: synthesising types at compile time
TypeScript's Pick, Omit, and Partial have direct C++26 equivalents. define_aggregate lets you construct a new type from a list of member specs — opening up type-level programming that was previously pure metaprogramming wizardry.
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Auto-generated mocks from interfaces
Mockito and Moq in C++: point a library at an abstract base class and get a mock that records calls and lets you program return values. No per-method MOCK_METHOD boilerplate.
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Autowired dependency injection: no container, just reflection
Spring's and .NET's DI containers, reimplemented as a 60-line C++26 library. Reflect constructor parameters, resolve them from a type registry, compose.
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A tiny ORM: struct to SQL via reflection
Diesel / Entity Framework ergonomics in C++: annotate a struct, generate CREATE TABLE, SELECT, INSERT, UPDATE, and a row-to-struct binder. No codegen tool, no intrusive macros.
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Revzin at C++Now: 'Reflection Is Only Half the Story' -- what generation looks like next
Barry Revzin's C++Now 2026 keynote (Mon 4 May, Aspen) landed the line the C++ reflection community has been circling for two years: C++26 reflection lets you OBSERVE -- the next question is what it looks like to GENERATE. The 90-minute talk is a tour of source-code-generation design space (macros, templates, Rust proc-macros, Swift macros, D mixins) and reads as the natural sequel to wro.cpp's whole 'Where this is heading' triptych framing.
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Clap for C++: turning structs into command-line parsers
Rust's clap-derive in C++: declare a struct, get a working argv parser with --flags, -short options, help text, subcommands. One attribute per field, zero manual dispatch.
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One codegen, many wire formats
JSON, YAML, XML, TOML, MessagePack — all from the same annotated struct. Factor format-specific syntax into a policy object, share the reflection walk, ship N formats for the cost of one.
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The five most useful things C++26 reflection unlocks (in effort order)
C++26 reflection looks like it requires a PhD in template metaprogramming. It does not. Five concrete projects you can build with it, ranked from five minutes to weeks -- use this as a triage when picking your first reflection-powered project.
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Deserialization and std::expected: completing the round-trip
Parse JSON into a typed C++ struct with precise per-field error reporting via std::expected. Reflection + template for + annotations — the same machinery, just running the other way.
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Annotations: tag-driven serialization comes to C++
P3394 brings serde-style and Jackson-style attribute programming to C++: rename, skip, skip_if_empty, rename_all — all as plain user-defined values queryable by reflection.
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Is std::vector consteval or constexpr? A reader's question, answered
A colleague asked: 'Is std::vector consteval and not constexpr?' Short answer: no, but the intuition is right. Long answer: the constexpr/consteval/constinit trio, the transient-allocation rule, and why std::define_static_array exists.
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A 40-line JSON serializer with reflection
Walking a struct and emitting JSON: the naive but complete version. About forty lines, no macros, no external codegen. The foundation of the reflect_json library.
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Deriving equality, hashing, and ordering from structure
C++20 gave us `= default` for operator== and <=>. Reflection lets us do the same for hashing, plus go beyond default: include/exclude fields, custom combinators, floating-point tolerances — all declarative.
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Auto-generating std::formatter<T> for any aggregate
Rust's #[derive(Debug)] in C++: make any struct printable via std::format and std::println by dropping in one partial specialisation of std::formatter. Nested types, containers, enum names — all handled.
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Goodbye magic_enum: enum reflection done right
A reflection-driven enum↔string library in 30 lines. No __PRETTY_FUNCTION__ tricks, no compile-time range knob, no compiler-specific behaviour — and unbounded, including enum values beyond 128.
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GCC 16.1 ships C++26 reflection -- your 30-line hands-on
GCC 16.1 dropped on 30 April 2026 with -freflection. C++26 was finalized at Croydon five weeks earlier. Here is a 25-line program you can compile and run today on your laptop.
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template for: iterating reflections at compile time
Expansion statements (proposal P1306) unroll a loop at compile time, instantiating the body once per element. They are the natural partner of reflection — one loop, N specialisations.
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C++26 is done -- five weeks since Croydon, here's what shipped
Five weeks ago WG21 voted C++26 to publication in Croydon. The dust has settled enough to take stock of what landed, what compiles today, and what it means for the wro.cpp reflection series.
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Splicing: [: r :] and putting reflections back into code
Splicing is the inverse of ^^: it takes a std::meta::info and drops the referred entity back into your source. Types, expressions, template arguments, member accesses — all round-trippable.
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Your first ^^: reflecting types and walking members
Hands-on introduction to C++26 reflection: the ^^ operator, std::meta::info, and walking struct members. We take the post-1 teaser apart and rebuild it from primitives.
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C++26 Reflection: What changes, and why it matters
Part 1 of the C++26 reflection series. A 40-line JSON serializer nobody could write in C++ before 2026 — plus the strategic story of why static reflection changes the ecosystem.