我在Go中的一个项目中有3个文件：
Cat.go

package entities

type Cat struct {
    Length              int
    Origin              string
    Image_link          string
    Family_friendly     int
    Shedding            int
    General_health      int
    Playfulness         int
    Children_friendly   int
    Grooming            int
    Intelligence        int
    Other_pets_friendly int
    Min_weight          int
    Max_weight          int
    Min_life_expectancy int
    Max_life_expectancy int
    Name                string
}

cat.repository.go

package src

import entities "src/domain/entitites"

type CatRepository interface {
    ListCats() []entities.Cat
}

cat.repository.impl.go

package repositories

import (
    entities "src/domain/entitites"
    nir "src/domain/repositories"
)

func (cat entities.Cat) ListCats() []entities.Cat {

}

我试图在第三个文件上实现接口，但编译器说“不能在非本地类型实体上定义新方法。Cat”
有人能告诉我怎么解决吗？