in src/generate.ts [288:296]
function addAssumedVariableDeclaration(type: reflect.Type, suffix = ''): Code {
let newType = type;
if (type.isInterfaceType() && !type.datatype) {
// guess corresponding non-interface type if possible
newType = guessConcreteType(type);
}
const variableName = escapeIdentifier(lowercaseFirstLetter(stripLeadingI(newType.name))) + suffix;
return new Code(variableName, [new Assumption(newType, variableName), new Import(newType)]);
}