[英]Assigning variable to a type in a function, how can I have the type itself be an input that will describe the type of a variable output? : Swift 5
我制作了一個包含數據、偏移量和讀取方法的文件讀取結構(不知何故 fread() 讓我感到困惑)。
我已經讓它工作了,現在想在其中實現一個方法,它將采用 nxm 矩陣項和 output 值矩陣。 (類似於 matlab 中的 fread(FileID, [ nm ], "(datatype)"))。
這是我的想法
// should be able to handle all sorts of datatypes and output n by m matrix.
mutating func matRead( dim : [[Int]], dtype : Int ){
if dim.count != 2{
fatalError("Dimensions dont match \"n by m\" in matRead")
}
// make sure to preallocate with zeros.
var mat_Out : typecast[dtype][2].self = []
}
我有一個看起來如此的類型轉換字典
// typecast dictionary key : [ array_type, byte, element_type ]
let typecast : [Int16:[Any]] = [ 1: [ [UInt8].self , 1, "uint8"],
2: [ [UInt16].self , 2, "uint16"], // use .self to reference data type itself.
3: [ [UInt32].self , 4, "uint32"],
4: [ [Int8].self , 1, "int8" ],
5: [ [Int16].self , 2, "int16" ],
6: [ [Int32].self , 4, "int32" ],
7: [ [Float32].self, 4, "float32"],
8: [ [Float64].self, 8, "float64"],
12:[ [Int32].self , 4, "int32" ] ]
這是問題: matRead() function 的第 8 行不起作用。 Swift 不明白我正在嘗試使用類型轉換字典將 output 矩陣分配給新的數組類型。 我也試過 "as" var mat_Out: Any = [] as typecast[dtype][0]
,同樣的錯誤(Swift 編譯器認為我的意思是把括號放在外面)。
或者,我可以 go 很長的路要走,然后根據字符串值手動進行類型轉換(已經必須這樣做:參見下面的 fread 結構代碼),但是如果有另一種方法,它將非常節省時間。
下面的 FileReading 結構(檢查計數的冗余使用,但我沒有清理它)
struct fRead {
var off : Int = 0
let data : Data
mutating func resetOffsetToZero() {
off = 0
}
mutating func setOffset( _ to : Int ) {
off.self = to
}
mutating func moveOffset( _ by : Int) {
off.self += by
}
func getOffset() -> Int {
return off
}
// reading without specified number of elements defaults to 1.
// these mutating funcs vary only in their output type and byte offset size.
mutating func int32Read(count : Int = 1) -> [Int32] {
var int32out : [Int32] = []
if count > 1 {
for i in 0...count-1 {
int32out.append( Int32( data.subdata(in: off + i * 4..<(off + (i + 1) * 4) ).withUnsafeBytes{ $0.load(as: Int32.self )} ))
}
off += count * 4
}
else if count == 1 {
int32out = [ Int32( data.subdata(in: off..<(off+4) ).withUnsafeBytes{ $0.load(as: Int32.self )} )]
off += 4
}
else if count == 0 {
return []
} else if count < 0{
print("Warning, fReadint32Read( count : Int = 1) called with a negative count, returning empty array.")
}
return int32out
}
mutating func int16Read(count : Int = 1) -> [Int16] {
var int16out : [Int16] = []
if count > 1 {
for i in 0...count-1 {
int16out.append( data.subdata(in: off + i * 2..<(off + (i + 1) * 2) ).withUnsafeBytes{ $0.load(as: Int16.self )} )
}
off += count * 2
}
else if count == 1 {
int16out = [ data.subdata(in: off..<(off+2) ).withUnsafeBytes{ $0.load(as: Int16.self )} ]
off += 2
}
else if count == 0 {
return []
} else if count < 0 {
print("Warning, fRead.int16Read( count : Int = 1) called with a negative count, returning empty array.")
}
return int16out
}
mutating func float64Read(count : Int = 1) -> [Float64] {
var float64out : [Float64] = []
if count > 1 {
for i in 0...count-1 {
float64out.append( data.subdata(in: off + i * 8..<(off + (i + 1) * 8) ).withUnsafeBytes{ $0.load(as: Float64.self )} )
}
off += count * 8
}
else if count == 1 {
float64out = [ data.subdata(in: off..<(off+8) ).withUnsafeBytes{ $0.load(as: Float64.self )} ]
off += 8
}
else if count == 0 {
return []
} else if count < 0 {
print("Warning, fRead.int16Read( count : Int = 1) called with a negative count, returning empty array.")
}
return float64out
}
mutating func uint32Read(count : Int = 1) -> [UInt32] {
var uint32out : [UInt32] = []
if count > 1 {
for i in 0...count-1 {
uint32out.append( data.subdata(in: off + i * 4..<(off + (i + 1) * 4) ).withUnsafeBytes{ $0.load(as: UInt32.self )} )
}
off += count * 4
}
else if count == 1 {
uint32out = [ data.subdata(in: off..<(off+4) ).withUnsafeBytes{ $0.load(as: UInt32.self )} ]
off += 4
}
else if count == 0 {
return []
} else if count < 0 {
print("Warning, fRead.int16Read( count : Int = 1) called with a negative count, returning empty array.")
}
return uint32out
}
mutating func int64Read(count : Int = 1) -> [Int64] {
var int64out : [Int64] = []
if count > 1 {
for i in 0...count-1 {
int64out.append( Int64( data.subdata(in: off + i * 4..<(off + (i + 1) * 8) ).withUnsafeBytes{ $0.load(as: Int64.self )} ))
}
off += count * 8
}
else if count == 1 {
int64out = [ Int64( data.subdata(in: off..<(off+8) ).withUnsafeBytes{ $0.load(as: Int64.self )} )]
off += 8
}
else if count == 0 {
return []
} else if count < 0{
print("Warning, fReadint64Read( count : Int = 1) called with a negative count, returning empty array.")
}
return int64out
}
// should be able to handle all sorts of datatypes and output n by m matrix.
mutating func matRead( dim : [[Int]], dtype : Int ){
if dim.count != 2{
fatalError("Dimensions dont match \"n by m\" in matRead")
}
// make sure to preallocate with zeros.
var mat_Out : Any = [] as typecast[dtype][0]
}
}
// I only discovered afterwards that 0...0 range works! So all the testing for ==1 , == 0 wasn't necessary
通用解決方案不是最好的方法嗎? 以下是元素為 integer 的通用版本,因此浮點數( BinaryFloatingPoint
)需要類似的 function 。
mutating func matRead<T: BinaryInteger>(count: Int = 1) -> [T] {
var intOut : [T] = []
let width = T().bitWidth / 8
if count > 1 {
for i in 0...count-1 {
intOut.append( T( data.subdata(in: off + i * 4..<(off + (i + 1) * width) ).withUnsafeBytes{ $0.load(as: T.self )} ))
}
off += count * width
}
else if count == 1 {
intOut = [ T( data.subdata(in: off..<(off+width) ).withUnsafeBytes{ $0.load(as: T.self )} )]
off += width
}
else if count == 0 {
return []
} else if count < 0{
print("Warning, fReadint64Read( count : Int = 1) called with a negative count, returning empty array.")
}
return intOut
}
請注意,上面的代碼中有一個“錯誤”,我不確定在i * 4..<(off + (i + 1)
中用什么替換 4,因為您在函數之間使用的數字如此不一致。我想它應該是width / 2
但我留給你更新那部分。
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