go spec: remove float, complex in favor of float64 and complex128

The default float type is not very useful but for the most basic applications.
For instance, as it is now, using the math package requires conversions for float
variables (the arguments for math functions are usually float64). Typical real
applications tend to specify the floating point precision required.

This proposal removes the predeclared types float and complex. Variable declarations
without type specification but with constant floating point or complex initializer
expressions will assume the type float64 or complex128 respectively.

The predeclared function cmplx is renamed to complex.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/3423041

doc/go_spec.html

@@ -1,5 +1,5 @@
 <!-- title The Go Programming Language Specification -->
-<!-- subtitle Version of January 13, 2011 -->
+<!-- subtitle Version of January 18, 2011 -->
 
 <!--
 TODO
@@ -11,7 +11,7 @@ TODO
     (struct{T} vs struct {T T} vs struct {t T})
 [ ] need explicit language about the result type of operations
 [ ] may want to have some examples for the types of shift operations
-[ ] should string(1<<s) and float(1<<s) be valid?
+[ ] should string(1<<s) and float32(1<<s) be valid?
 [ ] should probably write something about evaluation order of statements even
 	though obvious
 [ ] review language on implicit dereferencing
@@ -531,7 +531,7 @@ the result value of some built-in functions such as
 <code>cap</code> or <code>len</code> applied to
 <a href="#Length_and_capacity">some expressions</a>,
 <code>real</code> and <code>imag</code> applied to a complex constant
-and <code>cmplx</code> applied to numeric constants.
+and <code>complex</code> applied to numeric constants.
 The boolean truth values are represented by the predeclared constants
 <code>true</code> and <code>false</code>. The predeclared identifier
 <a href="#Iota">iota</a> denotes an integer constant.
@@ -700,8 +700,6 @@ There is also a set of predeclared numeric types with implementation-specific si
 <pre class="grammar">
 uint     either 32 or 64 bits
 int      same size as uint
-float    either 32 or 64 bits
-complex  real and imaginary parts have type float
 uintptr  an unsigned integer large enough to store the uninterpreted bits of a pointer value
 </pre>
 
@@ -871,8 +869,8 @@ struct {}
 // A struct with 6 fields.
 struct {
 	x, y int
-	u float
+	u float32
-	_ float  // padding
+	_ float32  // padding
 	A *[]int
 	F func()
 }
@@ -1007,10 +1005,10 @@ func()
 func(x int)
 func() int
 func(prefix string, values ...int)
-func(a, b int, z float) bool
+func(a, b int, z float32) bool
-func(a, b int, z float) (bool)
+func(a, b int, z float32) (bool)
-func(a, b int, z float, opt ...interface{}) (success bool)
+func(a, b int, z float64, opt ...interface{}) (success bool)
-func(int, int, float) (float, *[]int)
+func(int, int, float64) (float64, *[]int)
 func(n int) func(p *T)
 </pre>
 
@@ -1146,7 +1144,7 @@ failure will cause a <a href="#Run_time_panics">run-time panic</a>.
 
 <pre>
 map [string] int
-map [*T] struct { x, y float }
+map [*T] struct { x, y float64 }
 map [string] interface {}
 </pre>
 
@@ -1197,7 +1195,7 @@ A channel may be constrained only to send or only to receive by
 
 <pre>
 chan T         // can be used to send and receive values of type T
-chan&lt;- float   // can only be used to send floats
+chan&lt;- float64 // can only be used to send float64s
 &lt;-chan int     // can only be used to receive ints
 </pre>
 
@@ -1291,8 +1289,8 @@ type (
 	T1 []string
 	T2 struct { a, b int }
 	T3 struct { a, c int }
-	T4 func(int, float) *T0
+	T4 func(int, float64) *T0
-	T5 func(x int, y float) *[]string
+	T5 func(x int, y float64) *[]string
 )
 </pre>
 
@@ -1304,13 +1302,13 @@ these types are identical:
 T0 and T0
 []int and []int
 struct { a, b *T5 } and struct { a, b *T5 }
-func(x int, y float) *[]string and func(int, float) (result *[]string)
+func(x int, y float64) *[]string and func(int, float64) (result *[]string)
 </pre>
 
 <p>
 <code>T0</code> and <code>T1</code> are different because they are named types
-with distinct declarations; <code>func(int, float) *T0</code> and
+with distinct declarations; <code>func(int, float64) *T0</code> and
-<code>func(x int, y float) *[]string</code> are different because <code>T0</code>
+<code>func(x int, y float64) *[]string</code> are different because <code>T0</code>
 is different from <code>[]string</code>.
 </p>
 
@@ -1483,7 +1481,7 @@ Basic types:
 	int8 int16 int32 int64 string uint8 uint16 uint32 uint64
 
 Architecture-specific convenience types:
-	complex float int uint uintptr
+	int uint uintptr
 
 Constants:
 	true false iota
@@ -1492,7 +1490,7 @@ Zero value:
 	nil
 
 Functions:
-	append cap close closed cmplx copy imag len
+	append cap close closed complex copy imag len
 	make new panic print println real recover
 </pre>
 
@@ -1561,7 +1559,7 @@ const (
 	eof = -1             // untyped integer constant
 )
 const a, b, c = 3, 4, "foo"  // a = 3, b = 4, c = "foo", untyped integer and string constants
-const u, v float = 0, 3      // u = 0.0, v = 3.0
+const u, v float32 = 0, 3    // u = 0.0, v = 3.0
 </pre>
 
 <p>
@@ -1615,7 +1613,7 @@ const (
 
 const (
 	u         = iota * 42  // u == 0     (untyped integer constant)
-	v float = iota * 42  // v == 42.0  (float constant)
+	v float64 = iota * 42  // v == 42.0  (float64 constant)
 	w         = iota * 42  // w == 84    (untyped integer constant)
 )
 
@@ -1736,9 +1734,9 @@ VarSpec     = IdentifierList ( Type [ "=" ExpressionList ] | "=" ExpressionList
 
 <pre>
 var i int
-var U, V, W float
+var U, V, W float64
 var k = 0
-var x, y float = -1, -2
+var x, y float32 = -1, -2
 var (
 	i int
 	u, v, s = 2.0, 3.0, "bar"
@@ -1763,7 +1761,7 @@ of the expression list.
 <p>
 If the type is absent and the corresponding expression evaluates to an
 untyped <a href="#Constants">constant</a>, the type of the declared variable
-is <code>bool</code>, <code>int</code>, <code>float</code>, or <code>string</code>
+is <code>bool</code>, <code>int</code>, <code>float64</code>, or <code>string</code>
 respectively, depending on whether the value is a boolean, integer,
 floating-point, or string constant:
 </p>
@@ -1771,7 +1769,7 @@ floating-point, or string constant:
 <pre>
 var b = true    // t has type bool
 var i = 0       // i has type int
-var f = 3.0     // f has type float
+var f = 3.0     // f has type float64
 var s = "OMDB"  // s has type string
 </pre>
 
@@ -2132,11 +2130,11 @@ primes := []int{2, 3, 5, 7, 9, 11, 13, 17, 19, 991}
 // vowels[ch] is true if ch is a vowel
 vowels := [128]bool{'a': true, 'e': true, 'i': true, 'o': true, 'u': true, 'y': true}
 
-// the array [10]float{-1, 0, 0, 0, -0.1, -0.1, 0, 0, 0, -1}
+// the array [10]float32{-1, 0, 0, 0, -0.1, -0.1, 0, 0, 0, -1}
-filter := [10]float{-1, 4: -0.1, -0.1, 9: -1}
+filter := [10]float32{-1, 4: -0.1, -0.1, 9: -1}
 
 // frequencies in Hz for equal-tempered scale (A4 = 440Hz)
-noteFrequency := map[string]float{
+noteFrequency := map[string]float32{
 	"C0": 16.35, "D0": 18.35, "E0": 20.60, "F0": 21.83,
 	"G0": 24.50, "A0": 27.50, "B0": 30.87,
 }
@@ -2155,7 +2153,7 @@ FunctionLit = FunctionType Body .
 </pre>
 
 <pre>
-func(a, b int, z float) bool { return a*b &lt; int(z) }
+func(a, b int, z float64) bool { return a*b &lt; int(z) }
 </pre>
 
 <p>
@@ -2716,8 +2714,8 @@ var s uint = 33
 var i = 1&lt;&lt;s            // 1 has type int
 var j = int32(1&lt;&lt;s)     // 1 has type int32; j == 0
 var u = uint64(1&lt;&lt;s)    // 1 has type uint64; u == 1&lt;&lt;33
-var f = float(1&lt;&lt;s)   // illegal: 1 has type float, cannot shift
+var f = float32(1&lt;&lt;s)   // illegal: 1 has type float32, cannot shift
-var g = float(1&lt;&lt;33)  // legal; 1&lt;&lt;33 is a constant shift operation; g == 1&lt;&lt;33
+var g = float32(1&lt;&lt;33)  // legal; 1&lt;&lt;33 is a constant shift operation; g == 1&lt;&lt;33
 </pre>
 
 <h3 id="Operator_precedence">Operator precedence</h3>
@@ -3129,7 +3127,7 @@ type T struct {
 	a int
 }
 func (tv  T) Mv(a int)     int     { return 0 }  // value receiver
-func (tp *T) Mp(f float) float { return 1 }  // pointer receiver
+func (tp *T) Mp(f float32) float32 { return 1 }  // pointer receiver
 var t T
 </pre>
 
@@ -3174,7 +3172,7 @@ yields a function value representing <code>Mp</code> with signature
 </p>
 
 <pre>
-func(tp *T, f float) float
+func(tp *T, f float32) float32
 </pre>
 
 <p>
@@ -3422,14 +3420,14 @@ result is an untyped complex constant.
 Complex constants are always constructed from
 constant expressions involving imaginary
 literals or constants derived from them, or calls of the built-in function
-<a href="#Complex_numbers"><code>cmplx</code></a>.
+<a href="#Complex_numbers"><code>complex</code></a>.
 </p>
 
 <pre>
 const Σ = 1 - 0.707i
 const Δ = Σ + 2.0e-4 - 1/1i
 const Φ = iota * 1i
-const iΓ = cmplx(0, Γ)
+const iΓ = complex(0, Γ)
 </pre>
 
 <p>
@@ -3680,8 +3678,8 @@ In assignments, each value must be
 <a href="#Assignability">assignable</a> to the type of the
 operand to which it is assigned. If an untyped <a href="#Constants">constant</a>
 is assigned to a variable of interface type, the constant is <a href="#Conversions">converted</a>
-to type <code>bool</code>, <code>int</code>, <code>float</code>,
+to type <code>bool</code>, <code>int</code>, <code>float64</code>,
-<code>complex</code> or <code>string</code>
+<code>complex128</code> or <code>string</code>
 respectively, depending on whether the value is a boolean, integer, floating-point,
 complex, or string constant.
 </p>
@@ -3847,9 +3845,9 @@ case nil:
 	printString("x is nil")
 case int:
 	printInt(i)  // i is an int
-case float:
+case float64:
-	printFloat(i)  // i is a float
+	printFloat64(i)  // i is a float64
-case func(int) float:
+case func(int) float64:
 	printFunction(i)  // i is a function
 case bool, string:
 	printString("type is bool or string")  // i is an interface{}
@@ -3868,9 +3866,9 @@ if v == nil {
 	printString("x is nil")
 } else if i, is_int := v.(int); is_int {
 	printInt(i)  // i is an int
-} else if i, is_float := v.(float); is_float {
+} else if i, is_float64 := v.(float64); is_float64 {
-	printFloat(i)  // i is a float
+	printFloat64(i)  // i is a float64
-} else if i, is_func := v.(func(int) float); is_func {
+} else if i, is_func := v.(func(int) float64); is_func {
 	printFunction(i)  // i is a function
 } else {
 	i1, is_bool := v.(bool)
@@ -4189,7 +4187,7 @@ func simple_f() int {
 	return 2
 }
 
-func complex_f1() (re float, im float) {
+func complex_f1() (re float64, im float64) {
 	return -7.0, -4.0
 }
 </pre>
@@ -4201,7 +4199,7 @@ func complex_f1() (re float, im float) {
 		"return" statement listing these variables, at which point the
 		rules of the previous case apply.
 <pre>
-func complex_f2() (re float, im float) {
+func complex_f2() (re float64, im float64) {
 	return complex_f1()
 }
 </pre>
@@ -4212,7 +4210,7 @@ func complex_f2() (re float, im float) {
 		and the function may assign values to them as necessary.
 		The "return" statement returns the values of these variables.
 <pre>
-func complex_f3() (re float, im float) {
+func complex_f3() (re float64, im float64) {
 	re = 7.0
 	im = 4.0
 	return
@@ -4474,7 +4472,7 @@ For instance
 </p>
 
 <pre>
-type S struct { a int; b float }
+type S struct { a int; b float64 }
 new(S)
 </pre>
 
@@ -4593,29 +4591,28 @@ n3 := copy(b, "Hello, World!")  // n3 == 5, b == []byte("Hello")
 
 <p>
 Three functions assemble and disassemble complex numbers.
-The built-in function <code>cmplx</code> constructs a complex
+The built-in function <code>complex</code> constructs a complex
 value from a floating-point real and imaginary part, while
 <code>real</code> and <code>imag</code>
 extract the real and imaginary parts of a complex value.
 </p>
 
 <pre class="grammar">
-cmplx(realPart, imaginaryPart floatT) complexT
+complex(realPart, imaginaryPart floatT) complexT
 real(complexT) floatT
 imag(complexT) floatT
 </pre>
 
 <p>
 The type of the arguments and return value correspond.
-For <code>cmplx</code>, the two arguments must be of the same
+For <code>complex</code>, the two arguments must be of the same
 floating-point type and the return type is the complex type
 with the corresponding floating-point constituents:
-<code>complex</code> for <code>float</code>,
 <code>complex64</code> for <code>float32</code>,
 <code>complex128</code> for <code>float64</code>.
 The <code>real</code> and <code>imag</code> functions
 together form the inverse, so for a complex value <code>z</code>,
-<code>z</code> <code>==</code> <code>cmplx(real(z),</code> <code>imag(z))</code>.
+<code>z</code> <code>==</code> <code>complex(real(z),</code> <code>imag(z))</code>.
 </p>
 
 <p>
@@ -4624,12 +4621,12 @@ value is a constant.
 </p>
 
 <pre>
-var a = cmplx(2, -2)  // has type complex
+var a = complex(2, -2)             // complex128
-var b = cmplx(1.0, -1.4)  // has type complex
+var b = complex(1.0, -1.4)         // complex128
-x := float32(math.Cos(math.Pi/2))
+x := float32(math.Cos(math.Pi/2))  // float32
-var c64 = cmplx(5, -x)  // has type complex64
+var c64 = complex(5, -x)           // complex64
-var im = imag(b)  // has type float
+var im = imag(b)                   // float64
-var rl = real(c64)  // type float32
+var rl = real(c64)                 // float32
 </pre>
 
 <h3 id="Handling_panics">Handling panics</h3>
@@ -4984,7 +4981,7 @@ After
 </p>
 
 <pre>
-type T struct { i int; f float; next *T }
+type T struct { i int; f float64; next *T }
 t := new(T)
 </pre>