fosk 0.2.0

In-memory SQL-like query engine and lightweight data store for testing and prototyping.
Documentation 
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use crate::{
    JsonPrimitive,
    parser::{
        aggregators_helper::Accumulator,
        analyzer::{AnalysisContext, AnalyzerError},
        ast::Function,
    },
};

/// Per-aggregate metadata + factory.
/// One instance is registered globally per function name.
/// It is stateless and thread-safe to share.
pub trait AggregateImpl: Send + Sync {
    /// Canonical lowercase function name ("count", "sum", ...).
    fn name(&self) -> &'static str;

    /// Type inference for this function.
    /// - args are as in the parsed Function (qualified & folded already).
    /// - return (type, nullable)
    fn infer_type(
        &self,
        fun: &Function,
        ctx: &AnalysisContext,
    ) -> Result<(JsonPrimitive, bool), AnalyzerError>;

    /// Whether constant folding is allowed for this aggregate (usually false).
    fn allow_fold(&self) -> bool {
        false
    }

    /// Create a fresh accumulator instance for one group.
    fn create_accumulator(&self) -> Box<dyn Accumulator>;
}