Clean redundant generics params in Table (#234)

* Clean redundant generics params in Table

It is possible to use associated types the same way as generics parameters. In fact associated types are nothing more than better organized generics params. For example, there is no need to introduce another param to constraint iterator item to be Display, you can just say `where I::Iterator, I::Item: Display`. This allows to drop type params for Table from 5 to 2.

src/widgets/table.rs

@@ -12,10 +12,10 @@ use crate::style::Style;
 use crate::widgets::{Block, Widget};
 
 /// Holds data to be displayed in a Table widget
-pub enum Row<D, I>
+pub enum Row<D>
 where
-    D: Iterator<Item = I>,
-    I: Display,
+    D: Iterator,
+    D::Item: Display,
 {
     Data(D),
     StyledData(D, Style),
@@ -45,14 +45,7 @@ where
 ///     .style(Style::default().fg(Color::White))
 ///     .column_spacing(1);
 /// ```
-pub struct Table<'a, T, H, I, D, R>
-where
-    T: Display,
-    H: Iterator<Item = T>,
-    I: Display,
-    D: Iterator<Item = I>,
-    R: Iterator<Item = Row<D, I>>,
-{
+pub struct Table<'a, H, R> {
     /// A block to wrap the widget in
     block: Option<Block<'a>>,
     /// Base style for the widget
@@ -71,15 +64,12 @@ where
     rows: R,
 }
 
-impl<'a, T, H, I, D, R> Default for Table<'a, T, H, I, D, R>
+impl<'a, H, R> Default for Table<'a, H, R>
 where
-    T: Display,
-    H: Iterator<Item = T> + Default,
-    I: Display,
-    D: Iterator<Item = I>,
-    R: Iterator<Item = Row<D, I>> + Default,
+    H: Iterator + Default,
+    R: Iterator + Default,
 {
-    fn default() -> Table<'a, T, H, I, D, R> {
+    fn default() -> Table<'a, H, R> {
         Table {
             block: None,
             style: Style::default(),
@@ -92,20 +82,18 @@ where
         }
     }
 }
-
-impl<'a, T, H, I, D, R> Table<'a, T, H, I, D, R>
+impl<'a, H, D, R> Table<'a, H, R>
 where
-    T: Display,
-    H: Iterator<Item = T>,
-    I: Display,
-    D: Iterator<Item = I>,
-    R: Iterator<Item = Row<D, I>>,
+    H: Iterator,
+    D: Iterator,
+    D::Item: Display,
+    R: Iterator<Item = Row<D>>,
 {
-    pub fn new(header: H, rows: R) -> Table<'a, T, H, I, D, R> {
+    pub fn new(header: H, rows: R) -> Table<'a, H, R> {
         Table {
             block: None,
             style: Style::default(),
-            header,
+            header: header.into_iter(),
             header_style: Style::default(),
             widths: &[],
             rows,
@@ -113,25 +101,25 @@ where
             header_gap: 1,
         }
     }
-    pub fn block(mut self, block: Block<'a>) -> Table<'a, T, H, I, D, R> {
+    pub fn block(mut self, block: Block<'a>) -> Table<'a, H, R> {
         self.block = Some(block);
         self
     }
 
-    pub fn header<II>(mut self, header: II) -> Table<'a, T, H, I, D, R>
+    pub fn header<II>(mut self, header: II) -> Table<'a, H, R>
     where
-        II: IntoIterator<Item = T, IntoIter = H>,
+        II: IntoIterator<Item = H::Item, IntoIter = H>,
     {
         self.header = header.into_iter();
         self
     }
 
-    pub fn header_style(mut self, style: Style) -> Table<'a, T, H, I, D, R> {
+    pub fn header_style(mut self, style: Style) -> Table<'a, H, R> {
         self.header_style = style;
         self
     }
 
-    pub fn widths(mut self, widths: &'a [Constraint]) -> Table<'a, T, H, I, D, R> {
+    pub fn widths(mut self, widths: &'a [Constraint]) -> Table<'a, H, R> {
         let between_0_and_100 = |&w| match w {
             Constraint::Percentage(p) => p <= 100,
             _ => true,
@@ -144,37 +132,37 @@ where
         self
     }
 
-    pub fn rows<II>(mut self, rows: II) -> Table<'a, T, H, I, D, R>
+    pub fn rows<II>(mut self, rows: II) -> Table<'a, H, R>
     where
-        II: IntoIterator<Item = Row<D, I>, IntoIter = R>,
+        II: IntoIterator<Item = Row<D>, IntoIter = R>,
     {
         self.rows = rows.into_iter();
         self
     }
 
-    pub fn style(mut self, style: Style) -> Table<'a, T, H, I, D, R> {
+    pub fn style(mut self, style: Style) -> Table<'a, H, R> {
         self.style = style;
         self
     }
 
-    pub fn column_spacing(mut self, spacing: u16) -> Table<'a, T, H, I, D, R> {
+    pub fn column_spacing(mut self, spacing: u16) -> Table<'a, H, R> {
         self.column_spacing = spacing;
         self
     }
 
-    pub fn header_gap(mut self, gap: u16) -> Table<'a, T, H, I, D, R> {
+    pub fn header_gap(mut self, gap: u16) -> Table<'a, H, R> {
         self.header_gap = gap;
         self
     }
 }
 
-impl<'a, T, H, I, D, R> Widget for Table<'a, T, H, I, D, R>
+impl<'a, H, D, R> Widget for Table<'a, H, R>
 where
-    T: Display,
-    H: Iterator<Item = T>,
-    I: Display,
-    D: Iterator<Item = I>,
-    R: Iterator<Item = Row<D, I>>,
+    H: Iterator,
+    H::Item: Display,
+    D: Iterator,
+    D::Item: Display,
+    R: Iterator<Item = Row<D>>,
 {
     fn render(mut self, area: Rect, buf: &mut Buffer) {
         // Render block if necessary and get the drawing area