typescript中的interface&type

interface是真正的类型，type只是类型别名

inteface 遇到属性冲突会报错， type只会合并，遇到属性冲突会变成never类型

所以导致interface会”惰性求值”，而type会直接展开

type Wrapped = { value: T }; type Comparable = number | Wrapped; // ^^^^^^^^^^ // Type alias ‘Comparable’ circularly references itself.

typescript源码

getDeclaredTypeOfClassOrInterface

核心在这里： links.declaredType存在时，直接返回 links.declaredType

    function getDeclaredTypeOfClassOrInterface(symbol: Symbol): InterfaceType {
        let links = getSymbolLinks(symbol);
        const originalLinks = links;
        if (!links.declaredType) {
            const kind = symbol.flags & SymbolFlags.Class ? ObjectFlags.Class : ObjectFlags.Interface;
			     // ....
        }
        return links.declaredType as InterfaceType;
    }

对于type会尝试立即解析 getDeclaredTypeOfTypeAlias