这里有人可以看一下代码并告诉我它有什么问题吗?我本质上尝试构建几个对某些原始类型进行操作的通用函数,例如Int
, Float
, Double
etc.
不幸的是我无法让它正常工作。这是有效的代码(部分):
// http://stackoverflow.com/a/24047239/2282430
protocol SummableMultipliable: Equatable {
func +(lhs: Self, rhs: Self) -> Self
func *(lhs: Self, rhs: Self) -> Self
}
extension Double: SummableMultipliable {}
func vec_dot<T where T: SummableMultipliable>(a : [T], b: [T]) -> Double {
assert(a.count == b.count, "vectors must be of same length")
var s : Double = 0.0
for var i = 0; i < a.count; ++i {
let x = (a[i] * b[i]) as Double
s = s + x
}
return s
}
现在当我写:
var doubleVec : [Double] = [1,2,3,4]
vec_dot(doubleVec, doubleVec)
它返回正确的结果30
。好的,到目前为止一切顺利。当我尝试传递一系列时,事情变得很奇怪Int
s:
extension Int : SummableMultipliable {}
var intVec : [Int] = [1,2,3,4]
vec_dot(intVec, intVec)
嘭!抛出异常:
let x = (a[1] * b[1]) as Double
* thread #1: tid = 0x139dd0, 0x00000001018527ad libswiftCore.dylib`swift_dynamicCast + 1229, queue = 'com.apple.main-thread', stop reason = EXC_BREAKPOINT (code=EXC_I386_BPT, subcode=0x0)
* frame #0: 0x00000001018527ad libswiftCore.dylib`swift_dynamicCast + 1229
frame #1: 0x000000010d6c3a09 $__lldb_expr248`__lldb_expr_248.vec_dot <A : __lldb_expr_248.SummableMultipliable>(a=Swift.Array<T> at 0x00007fff5e5a9648, b=Swift.Array<T> at 0x00007fff5e5a9640) -> Swift.Double + 921 at playground248.swift:54
frame #2: 0x000000010d6c15b0 $__lldb_expr248`top_level_code + 1456 at playground248.swift:64
frame #3: 0x000000010d6c4561 $__lldb_expr248`main + 49 at <EXPR>:0
frame #4: 0x000000010165b390 FirstTestPlayground`get_field_types__XCPAppDelegate + 160
frame #5: 0x000000010165bea1 FirstTestPlayground`reabstraction thunk helper from @callee_owned () -> (@unowned ()) to @callee_owned (@in ()) -> (@out ()) + 17
frame #6: 0x000000010165ab61 FirstTestPlayground`partial apply forwarder for reabstraction thunk helper from @callee_owned () -> (@unowned ()) to @callee_owned (@in ()) -> (@out ()) + 81
frame #7: 0x000000010165bed0 FirstTestPlayground`reabstraction thunk helper from @callee_owned (@in ()) -> (@out ()) to @callee_owned () -> (@unowned ()) + 32
frame #8: 0x000000010165bf07 FirstTestPlayground`reabstraction thunk helper from @callee_owned () -> (@unowned ()) to @callee_unowned @objc_block () -> (@unowned ()) + 39
frame #9: 0x0000000101fedaac CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 12
frame #10: 0x0000000101fe37f5 CoreFoundation`__CFRunLoopDoBlocks + 341
frame #11: 0x0000000101fe2fb3 CoreFoundation`__CFRunLoopRun + 851
frame #12: 0x0000000101fe29f6 CoreFoundation`CFRunLoopRunSpecific + 470
frame #13: 0x000000010208f2b1 CoreFoundation`CFRunLoopRun + 97
frame #14: 0x0000000101658be8 FirstTestPlayground`top_level_code + 3784
frame #15: 0x000000010165b3ba FirstTestPlayground`main + 42
frame #16: 0x0000000103cd9145 libdyld.dylib`start + 1
我尝试执行不同的转换:
let x = Double(a[i] * b[1])
Error:找不到接受提供的参数的“init”重载。
let y = a[i] * b[1]
let x = Double(y)
Error:无法使用“T”类型的参数调用“init”。
接下来,我尝试了:
let y = Double(a[i]) * Double(b[1])
let x = y
Error:无法使用“(Double, Double”) 类型的参数列表调用“*”。
我尝试过many更多的东西。当我尝试通过时Int
作为泛型类型,没有任何作用了。
也许我只是错过了一些基本的东西,或者我太笨了,无法理解通用编程。在 C++ 中,我会在 2 秒内完成。