Question 1

How do I serialize a robin-map to a file in C++?

Accepted Answer

Use the built-in serialize method with custom serializer and deserializer function objects. The README provides an example using file streams for arithmetic types, ensuring efficient binary serialization with optional hash compatibility for faster deserialization.

Question 2

What are the main differences between robin-map and std::unordered_map?

Accepted Answer

Robin-map uses robin hood hashing for better performance, has different iterator invalidation rules (invalidates on any modification), lacks bucket methods, and requires .value() to modify values through iterators. It also adds features like serialization and heterogeneous lookups.

Question 3

Should I use robin-map or absl::flat_hash_map for my C++ project?

Accepted Answer

Both offer high performance, but robin-map provides built-in serialization and more flexible heterogeneous lookups, while absl::flat_hash_map is part of Abseil with wider ecosystem support. Benchmark both for your specific use case, as performance can vary based on hash functions and growth policies.

Question 4

How can I use robin-map with smart pointers as keys?

Accepted Answer

Enable heterogeneous lookups by using std::equal_to<> or a custom KeyEqual with an is_transparent member. This allows finding keys with raw pointers or other types without constructing smart pointers, as shown in the README's heterogeneous lookups example.

Question 5

Why is my robin-map slow when inserting integer keys?

Accepted Answer

This could be due to poor hash function distribution, especially with the power-of-two growth policy. Switch to the prime growth policy version (robin_pg_map) or use a better hash function to avoid collisions, as highlighted in the performance pitfalls section.

Question 6

How to install robin-map using CMake?

Accepted Answer

Add the include directory manually or use the provided CMakeLists.txt with target_link_libraries. For example, use add_subdirectory on the robin-map directory and link your target to tsl::robin_map, as detailed in the installation section.

Question 7

Can robin-map be used in a project with exceptions disabled?

Accepted Answer

Yes, compile with -fno-exceptions on Clang/GCC, without /EH on MSVC, or define TSL_NO_EXCEPTIONS. The library will use std::terminate instead of throw, making it compatible with exception-free environments.

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