avro_schema

Helper macro to define a static Avro schema using the builder pattern.

This creates a OnceLock that initializes the schema exactly once and returns a &‘static str reference.

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Limitation: one schema per macro call site, not per type

The plain form avro_schema!(builder) expands to a single static at the call site. Rust has no generic statics, so inside a generic function or a generic impl every instantiation shares that one static: the first instantiation to run builds the schema and every other type parameter gets the same string back, even when its builder expression would produce a different schema. Use the plain form only where the schema does not depend on a type parameter.

Where it does, use the keyed form avro_schema!(for T => builder), which caches one schema per T (keyed by TypeId, so T: ‘static). Each distinct schema is built once and its string lives for the rest of the program, the same as with the plain form.

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Example

use gpudb_api::{avro_schema, avro_schema_builder::{AvroSchemaBuilder, AvroType}};

fn my_schema() -> &'static str {
    avro_schema!(
        AvroSchemaBuilder::new("MyRecord")
            .int_field("id")
            .string_field("name")
            .bytes_field("payload")
    )
}

A schema that varies with a type parameter:

use gpudb_api::{avro_schema, avro_schema_builder::AvroSchemaBuilder};

fn schema_for<T: 'static>() -> &'static str {
    avro_schema!(for T =>
        AvroSchemaBuilder::new(std::any::type_name::<T>().replace("::", "_"))
            .int_field("id")
    )
}

assert_ne!(schema_for::<u8>(), schema_for::<u16>());