set nil as the initial value of the struct reference type fields (#192)

gm/basicgm.v

@@ -15,8 +15,8 @@ pub mut:
 @[heap]
 pub struct Segment {
 pub:
-	a &Point
-	b &Point
+	a &Point = unsafe { nil }
+	b &Point = unsafe { nil }
 }
 
 // Point.new creates a new point

ml/data.v

@@ -25,8 +25,8 @@ pub mut:
 	observable  util.Observable = util.Observable{}
 	nb_samples  int // number of data points (samples). number of rows in x and y
 	nb_features int // number of features. number of columns in x
-	x           &la.Matrix[T] // [nb_samples][nb_features] x values
-	y           []T // [nb_samples] y values [optional]
+	x           &la.Matrix[T] = unsafe { nil } // [nb_samples][nb_features] x values
+	y           []T           // [nb_samples] y values [optional]
 }
 
 // Data.new returns a new object to hold ML data

ml/kmeans.v

@@ -10,10 +10,10 @@ import vsl.plot
 pub struct Kmeans {
 mut:
 	name       string     // name of this "observer"
-	data       &Data[f64] // x data
-	stat       &Stat[f64] // statistics about x (data)
+	data       &Data[f64] = unsafe { nil } // x data
+	stat       &Stat[f64] = unsafe { nil } // statistics about x (data)
 	nb_classes int        // expected number of classes
-	bins       &gm.Bins   // "bins" to speed up searching for data points given their coordinates (2D or 3D only at the moment)
+	bins       &gm.Bins = unsafe { nil } // "bins" to speed up searching for data points given their coordinates (2D or 3D only at the moment)
 	nb_iter    int        // number of iterations
 pub mut:
 	classes    []int   // [nb_samples] indices of classes of each sample

ml/knn.v

@@ -9,7 +9,7 @@ import vsl.plot
 pub struct KNN {
 mut:
 	name    string // name of this "observer"
-	data    &Data[f64]
+	data    &Data[f64] = unsafe { nil }
 	weights map[f64]f64 // weights[class] = weight
 pub mut:
 	neighbors []Neighbor

ml/linreg.v

@@ -10,12 +10,12 @@ pub struct LinReg {
 mut:
 	// main
 	name string     // name of this "observer"
-	data &Data[f64] // x-y data
+	data &Data[f64] = unsafe { nil } // x-y data
 	// workspace
 	e []f64 // vector e = b⋅o + x⋅theta - y [nb_samples]
 pub mut:
-	stat   &Stat[f64] // statistics
-	params &ParamsReg[f64]
+	stat   &Stat[f64]      = unsafe { nil } // statistics
+	params &ParamsReg[f64] = unsafe { nil }
 }
 
 // LinReg.new returns a new LinReg object

ml/workspace.v

@@ -11,7 +11,7 @@ import vsl.la
 @[heap]
 pub struct Stat[T] {
 pub mut:
-	data   &Data[T] // data
+	data   &Data[T] = unsafe { nil } // data
 	name   string   // name of this object
 	min_x  []T      // [n_features] min x values
 	max_x  []T      // [n_features] max x values

vcl/buffer.c.v

@@ -3,7 +3,7 @@ module vcl
 // Buffer memory buffer on the device
 struct Buffer {
 	size   int
-	device &Device
+	device &Device = unsafe { nil }
 mut:
 	memobj ClMem
 }

vcl/bytes.c.v

@@ -2,7 +2,7 @@ module vcl
 
 // Bytes is a memory buffer on the device that holds []byte
 pub struct Bytes {
-	buf &Buffer
+	buf &Buffer = unsafe { nil }
 }
 
 // bytes allocates new memory buffer with specified size on device

vcl/image.c.v

@@ -21,7 +21,7 @@ pub interface IImage {
 // Image memory buffer on the device with image data
 pub struct Image {
 	format   ClImageFormat
-	desc     &ClImageDesc
+	desc     &ClImageDesc = unsafe { nil }
 	img_data voidptr
 mut:
 	buf &Buffer

vcl/kernel.c.v

@@ -46,7 +46,7 @@ fn UnsupportedArgumentTypeError.new(index int, value ArgumentType) IError {
 
 // Kernel represent a single kernel
 pub struct Kernel {
-	d &Device
+	d &Device = unsafe { nil }
 	k ClKernel
 }
 
@@ -61,7 +61,7 @@ pub fn (k &Kernel) global(global_work_sizes ...int) KernelWithGlobal {
 // KernelWithGlobal is a kernel with the global size set
 // to run the kernel it must also set the local size
 pub struct KernelWithGlobal {
-	kernel            &Kernel
+	kernel            &Kernel = unsafe { nil }
 	global_work_sizes []int
 }
 
@@ -77,7 +77,7 @@ pub fn (kg KernelWithGlobal) local(local_work_sizes ...int) KernelCall {
 // KernelCall is a kernel with global and local work sizes set
 // and it's ready to be run
 pub struct KernelCall {
-	kernel            &Kernel
+	kernel            &Kernel = unsafe { nil }
 	global_work_sizes []int
 	local_work_sizes  []int
 }

vcl/vector.c.v

@@ -3,7 +3,7 @@ module vcl
 // Vector is a memory buffer on device that holds []T
 pub struct Vector[T] {
 mut:
-	buf &Buffer
+	buf &Buffer = unsafe { nil }
 }
 
 // vector allocates new vector buffer with specified length