You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: info.rs
    path of file: ./repos/wasmtime/crates/environ/src/component
    
    the code of the file until where you have to start completion: // General runtime type-information about a component.
//
// Compared to the `Module` structure for core wasm this type is pretty
// significantly different. The core wasm `Module` corresponds roughly 1-to-1
// with the structure of
    
    pub fn map_index<U>(self, f: impl FnOnce(T) -> U) -> CoreExport<U> {
        CoreExport {
            instance: self.instance,
            item: match self.item {
                ExportItem::Index(i) => ExportItem::Index(f(i)),
                ExportItem::Name(s) => ExportItem::Name(s),
            },
        }
    }