Add struct constraint to generic type parameter

Author: dpanfilyonok

src/GraphBLAS-sharp/CSRMatrix.fs

@@ -19,7 +19,7 @@ with
         ColumnCount = 0
     }
 
-type CSRMatrix<'a>(csrTuples: CSRFormat<'a>) =
+type CSRMatrix<'a when 'a : struct>(csrTuples: CSRFormat<'a>) =
     inherit Matrix<'a>()
 
     let rowCount = csrTuples.RowPointers.Length - 1

src/GraphBLAS-sharp/DenseVector.fs

@@ -1,6 +1,6 @@
 namespace GraphBLAS.FSharp
 
-type DenseVector<'a>(vector: 'a[]) =
+type DenseVector<'a when 'a : struct>(vector: 'a[]) =
     inherit Vector<'a>()
 
     new() = DenseVector(Array.zeroCreate<'a> 0)

src/GraphBLAS-sharp/MatrixAndVector.fs

@@ -1,7 +1,7 @@
 namespace GraphBLAS.FSharp
 
 [<AbstractClass>]
-type Matrix<'a>() =
+type Matrix<'a when 'a : struct>() =
     abstract RowCount: int
     abstract ColumnCount: int
     abstract Mask: Mask2D
@@ -34,7 +34,7 @@ type Matrix<'a>() =
     static member inline (.+) (x: Matrix<'a>, y: Matrix<'a>) = x.EWiseAddInplace y
     static member inline (.*) (x: Matrix<'a>, y: Matrix<'a>) = x.EWiseMultInplace y
 
-and [<AbstractClass>] Vector<'a>() =
+and [<AbstractClass>] Vector<'a when 'a : struct>() =
     abstract Length: int
     abstract Mask: Mask1D
     abstract AsArray: 'a[]

src/GraphBLAS-sharp/Scalar.fs

@@ -1,5 +1,5 @@
 namespace GraphBLAS.FSharp
 
-type Scalar<'a> = Scalar of 'a
+type Scalar<'a when 'a : struct> = Scalar of 'a
 with
     static member op_Implicit (Scalar source) = source