Merge pull request #43 from phip1611/fix-scaling-function-type

better spectrum scaling function type

src/lib.rs

@@ -176,7 +176,7 @@ pub fn samples_fft_to_spectrum(
     samples: &[f32],
     sampling_rate: u32,
     frequency_limit: FrequencyLimit,
-    scaling_fn: Option<SpectrumScalingFunction>,
+    scaling_fn: Option<&SpectrumScalingFunction>,
 ) -> Result<FrequencySpectrum, SpectrumAnalyzerError> {
     // everything below two samples is unreasonable
     if samples.len() < 2 {
@@ -247,7 +247,7 @@ fn fft_result_to_spectrum(
     fft_result: &[Complex32],
     sampling_rate: u32,
     frequency_limit: FrequencyLimit,
-    scaling_fn: Option<SpectrumScalingFunction>,
+    scaling_fn: Option<&SpectrumScalingFunction>,
 ) -> Result<FrequencySpectrum, SpectrumAnalyzerError> {
     let maybe_min = frequency_limit.maybe_min();
     let maybe_max = frequency_limit.maybe_max();

src/scaling.rs

@@ -52,8 +52,8 @@ pub struct SpectrumDataStats {
 
 /// Describes the type for a function that scales/normalizes the data inside [`crate::FrequencySpectrum`].
 /// The scaling only affects the value/amplitude of the frequency, but not the frequency itself.
-/// It gets applied to every single element.
-/// ///
+/// It is applied to every single element.
+///
 /// A scaling function can be used for example to subtract the minimum (`min`) from each value.
 /// It is optional to use the second parameter [`SpectrumDataStats`].
 /// and the type works with static functions as well as dynamically created closures.
@@ -64,7 +64,7 @@ pub struct SpectrumDataStats {
 ///
 /// This uses `f32` in favor of [`crate::FrequencyValue`] because the latter led to
 /// some implementation problems.
-pub type SpectrumScalingFunction<'a> = &'a dyn Fn(f32, &SpectrumDataStats) -> f32;
+pub type SpectrumScalingFunction = dyn Fn(f32, &SpectrumDataStats) -> f32;
 
 /// Calculates the base 10 logarithm of each frequency magnitude and
 /// multiplies it with 20. This scaling is quite common, you can
@@ -136,14 +136,14 @@ pub fn divide_by_N_sqrt(val: f32, stats: &SpectrumDataStats) -> f32 {
 
 /// Combines several scaling functions into a new single one.
 ///
+/// Currently there is the limitation that the functions need to have
+/// a `'static` lifetime. This will be fixed if someone needs this.
+///
 /// # Example
 /// ```ignored
-/// Some(&combined(&[&divide_by_N, &scale_20_times_log10]))
+/// let fncs = combined(&[&divide_by_N, &scale_20_times_log10]);
 /// ```
-#[allow(clippy::type_complexity)]
-pub fn combined<'a>(
-    fncs: &'a [SpectrumScalingFunction<'a>],
-) -> Box<dyn Fn(f32, &SpectrumDataStats) -> f32 + 'a> {
+pub fn combined(fncs: &'static [&SpectrumScalingFunction]) -> Box<SpectrumScalingFunction> {
     Box::new(move |val, stats| {
         let mut val = val;
         for fnc in fncs {
@@ -169,7 +169,7 @@ mod tests {
             n: data.len() as f32,
         };
         // check that type matches
-        let scaling_fn: SpectrumScalingFunction = &scale_to_zero_to_one;
+        let scaling_fn: &SpectrumScalingFunction = &scale_to_zero_to_one;
         let scaled_data = data
             .into_iter()
             .map(|x| scaling_fn(x, &stats))
@@ -179,4 +179,22 @@ mod tests {
             float_cmp::approx_eq!(f32, *expected_val, *actual_val, ulps = 3);
         }
     }
+
+    // make sure this compiles
+    #[test]
+    fn test_combined_compiles() {
+        let _combined_static = combined(&[&scale_20_times_log10, &divide_by_N, &divide_by_N_sqrt]);
+
+        // doesn't compile yet.. fix this once someone requests it
+        /*let closure_scaling_fnc = |frequency_magnitude: f32, _stats: &SpectrumDataStats| {
+           0.0
+        };
+
+        let _combined_dynamic = combined(&[
+            &scale_20_times_log10,
+            &divide_by_N,
+            &divide_by_N_sqrt,
+            &closure_scaling_fnc,
+        ]);*/
+    }
 }

src/spectrum.rs

@@ -116,7 +116,7 @@ impl FrequencySpectrum {
     #[inline(always)]
     pub fn apply_scaling_fn(
         &self,
-        scaling_fn: SpectrumScalingFunction,
+        scaling_fn: &SpectrumScalingFunction,
     ) -> Result<(), SpectrumAnalyzerError> {
         {
             // drop RefMut<> from borrow_mut() before calc_statistics