Fixes to Histogram

1. Now histograms with more than 31 bins are supported (before there
   were issues with missing implementations on arrays.)
2. The items defined by `define_histogram!` are in their own module, to
   avoid issues with Rust's lack of macro hygiene for items.

src/histogram.rs

@@ -1,13 +1,20 @@
 /// Define a histogram with a number of bins known at compile time.
 ///
+/// Because macros are not hygenic for items, everything is defined in a private
+/// module with the given name. This includes the `Histogram` struct, the number
+/// of bins `LEN` and the histogram iterator `HistogramIter`.
+///
+///
+/// # Example
+///
 /// ```
 /// # extern crate core;
 /// # #[macro_use] extern crate average;
 /// # fn main() {
 /// use average::Histogram;
 ///
-/// define_histogram!(Histogram10, 10);
+/// define_histogram!(hist, 10);
-/// let mut h = Histogram10::with_const_width(0., 100.);
+/// let mut h = hist::Histogram::with_const_width(0., 100.);
 /// for i in 0..100 {
 ///     h.add(i as f64).unwrap();
 /// }
@@ -17,19 +24,33 @@
 #[macro_export]
 macro_rules! define_histogram {
     ($name:ident, $LEN:expr) => (
+        mod $name {
+            use $crate::Histogram as Trait;
+
             /// The number of bins of the histogram.
             const LEN: usize = $LEN;
 
             /// A histogram with a number of bins known at compile time.
-        #[derive(Debug, Clone)]
+            #[derive(Clone)]
-        pub struct $name {
+            pub struct Histogram {
                 /// The ranges defining the bins of the histogram.
                 range: [f64; LEN + 1],
                 /// The bins of the histogram.
                 bin: [u64; LEN],
             }
 
-        impl $name {
+            impl ::core::fmt::Debug for Histogram {
+                fn fmt(&self, formatter: &mut ::core::fmt::Formatter)
+                    -> ::core::fmt::Result {
+                    write!(formatter, "Histogram {{ range: ")?;
+                    self.range[..].fmt(formatter)?;
+                    write!(formatter, ", bins: ")?;
+                    self.bin[..].fmt(formatter)?;
+                    write!(formatter, " }}")
+                }
+            }
+
+            impl Histogram {
                 /// Construct a histogram with constant bin width.
                 #[inline]
                 pub fn with_const_width(start: f64, end: f64) -> Self {
@@ -170,7 +191,7 @@ macro_rules! define_histogram {
                 }
             }
 
-        impl<'a> ::core::iter::IntoIterator for &'a $name {
+            impl<'a> ::core::iter::IntoIterator for &'a Histogram {
                 type Item = ((f64, f64), u64);
                 type IntoIter = IterHistogram<'a>;
                 fn into_iter(self) -> IterHistogram<'a> {
@@ -181,24 +202,26 @@ macro_rules! define_histogram {
                 }
             }
 
-        impl $crate::Histogram for $name {
+            impl $crate::Histogram for Histogram {
                 #[inline]
                 fn bins(&self) -> &[u64] {
                     &self.bin as &[u64]
                 }
             }
 
-        impl<'a> ::core::ops::AddAssign<&'a Self> for $name {
+            impl<'a> ::core::ops::AddAssign<&'a Self> for Histogram {
                 #[inline]
                 fn add_assign(&mut self, other: &Self) {
-                assert_eq!(self.range, other.range);
+                    for (a, b) in self.range.iter().zip(other.range.iter()) {
+                        assert_eq!(a, b, "Both histograms must have the same ranges");
+                    }
                     for (x, y) in self.bin.iter_mut().zip(other.bin.iter()) {
                         *x += y;
                     }
                 }
             }
 
-        impl ::core::ops::MulAssign<u64> for $name {
+            impl ::core::ops::MulAssign<u64> for Histogram {
                 #[inline]
                 fn mul_assign(&mut self, other: u64) {
                     for x in self.bin.iter_mut() {
@@ -207,7 +230,7 @@ macro_rules! define_histogram {
                 }
             }
 
-        impl $crate::Merge for $name {
+            impl $crate::Merge for Histogram {
                 fn merge(&mut self, other: &Self) {
                     assert_eq!(self.bin.len(), other.bin.len());
                     for (a, b) in self.range.iter().zip(other.range.iter()) {
@@ -218,5 +241,6 @@ macro_rules! define_histogram {
                     }
                 }
             }
+        }
     );
 }

src/lib.rs

@@ -64,7 +64,7 @@
 //!
 //! The [`define_histogram`] macro can be used to define a histogram struct that
 //! uses constant memory. See [`Histogram10`] (defined using
-//! `define_histogram!(Histogram10, 10)`) and the extension trait [`Histogram`]
+//! `define_histogram!(..., 10)`) and the extension trait [`Histogram`]
 //! for the methods available to the generated struct.
 //!
 //!
@@ -110,5 +110,6 @@ pub use minmax::{Min, Max};
 pub use quantile::Quantile;
 pub use traits::{Estimate, Merge, Histogram};
 
-define_histogram!(Histogram10, 10);
+define_histogram!(hist, 10);
+pub use hist::Histogram as Histogram10;
 define_moments!(Moments4, 4);

tests/histogram.rs

@@ -9,7 +9,10 @@ use rand::FromEntropy;
 
 use average::{Histogram, Merge};
 
-define_histogram!(Histogram10, 10);
+define_histogram!(hist10, 10);
+define_histogram!(hist100, 100);
+
+use hist10::Histogram as Histogram10;
 
 #[test]
 fn with_const_width() {