I'm trying to make a Graph
class with an outEdges
method (just for the purpose of learning Swift, not because I need a Graph class).
我尝试用一个outEdges方法来创建一个图形类(只是为了学习Swift,而不是因为我需要一个图形类)。
I thought I could use .filter()
to implement the outEdges method, but I get this error:
我认为我可以使用.filter()来实现outEdges方法,但是我得到了这个错误:
error: cannot convert value of type '([V]) -> Bool' to expected argument type '([_]) -> Bool'
return edges.filter(leftVertexIs(v))
^~~~~~~~~~~~~~~
With this code:
这段代码:
class Graph<V: Equatable> {
var edges = [[V]]()
func addEdge(v1: V, _ v2: V) -> Graph<V> {
edges.append([v1, v2])
return self
}
func leftVertexIs(v: V) -> (([V]) -> Bool) {
return {(e: [V]) -> Bool in return e[0] == v}
}
func outEdges(v: V) -> [V] {
return edges.filter(leftVertexIs(v))
}
}
var g = Graph<Int>()
g.addEdge(2, 4).addEdge(4, 6).addEdge(3, 5).addEdge(2, 7)
g.outEdges(2)
(Note: I moved the filter predicate into a closure to ensure it was working properly)
(注意:我将filter谓词移动到闭包中,以确保它正常工作)
1 个解决方案
#1
2
edges
has the type [[V]]
, then edges.filter()
has the same type and that should be the return type of outEdges
:
边缘具有类型[V],然后edgs .filter()具有相同类型,应该是outEdges的返回类型:
func outEdges(v: V) -> [[V]] {
return edges.filter(leftVertexIs(v))
}
Remark: Instead of storing each edge as a two-element array you should consider to use a tuple (left : V , right : V)
or a struct
instead.
注意:与其将每条边存储为两个元素数组,不如考虑使用tuple(左:V,右:V)或struct。
#1
2
edges
has the type [[V]]
, then edges.filter()
has the same type and that should be the return type of outEdges
:
边缘具有类型[V],然后edgs .filter()具有相同类型,应该是outEdges的返回类型:
func outEdges(v: V) -> [[V]] {
return edges.filter(leftVertexIs(v))
}
Remark: Instead of storing each edge as a two-element array you should consider to use a tuple (left : V , right : V)
or a struct
instead.
注意:与其将每条边存储为两个元素数组,不如考虑使用tuple(左:V,右:V)或struct。